Sections
The short answer is that it is traditional in intro astro textbooks to do so.
Going back to back to Stonehenge is very traditional: see the figure below (local link / general link: sullivan_stonehenge_003_remains.html).
php require("/home/jeffery/public_html/astro/stonehenge/sullivan_stonehenge_003_remains_2.html");?>
But why is the history of astronomy to
Newton traditional?
There are two rationales:
One of the general learning outcomes of an introductory astronomy is to learn something about how science is done. One aspect of learning how science is done is to see scientific method in action: a cycle of theory and observation/experiment leading to progress in understanding nature: see the figure below (local link / general link: sci_method.html).
php require("/home/jeffery/public_html/astro/science/sci_method.html");?>
The history of astronomy to
Newton
is the grand classical example of the
scientific method
in action.
However, the history of astronomy to Newton is NOT a typical exmple of the scientific method in action.
The history stretches over millennia and most of the participants were unaware of the roles they were playing in the scientific method---the scientific method was first explictily expressed in the 17th century as illustrated by the quote from Robert Hooke (1635--1703) in the figure above (local link / general link: sci_method.html).
In some cases, the participants in the history of astronomy to Newton may have thought that they were establishing truth for all time at least insofar as human reason could reach.
In some cases, they may have thought that truth was beyond human capabilities, and all that could be done is give a satisfying-to-reason explanation of how things could be: i.e., a rational myth.
A modern perspective is that final truth may beyond human capabilities, but there may be no limit it seems to how much we can improve our understanding.
Note that others earlier in the 17th century before Robert Hooke's (1635--1703) statement exemplified the scientific method in their work: outstandingly Galileo (1564--1642) and Johannes Kepler (1571--1630).
Before 17th century, the scientific method was certainly practiced sometimes (e.g., Archimedes (c.287--c.212 BCE)), but it was NOT recognized as a prime rule of science.
Certainly, effective recognition of the scientific method was a key ingredient in the Scientific Revolution (c.1543--c.1687), and so a key ingredient in the modern history (c.1500--present) since then.
First note that the nature and meaning of everything just
is an intrinsic vital human concern.
Now cosmology
(the science of the universe
as whole)
is NOT
the science of everything of course, but it is the science of the largest scale
of everything, and so attracts special interest---like
elephants and
whales---but more so since
we are in universe and
sustained by it.
It also seems reasonable that the largest scale will be vital for "meaning of", NOT just "nature of".
See pondering the universe
in the figure below
(local link /
general link: infinity_eternity.html).
The upshot so far is that
cosmology
is itself a vital human concern.
Given that, the history of how we got to where we are today
in cosmology
starting from
mythological cosmology
becomes its own vital human concern---an aspect of
cultural history.
The history is always seen as a big part.
It is NOT outmoded.
Now the history of astronomy to
Newton
is essentially the history
of cosmology
to
Newton.
At every stage, the
astronomers
were studying the universe
as they perceived it.
In fact until
circa 1600,
they mostly studied Solar System.
The Solar System was just most of
cosmology as it was
understood until circa 1600.
So we study the
history of astronomy
to Newton
in order to study the
history of cosmology
to Newton
(see the figure below:
local link /
general link: newton_principia.html).
We have enough astronomy lore now to
understand the history of cosmology
to Newton.
One needs to learn more
astronomy lore
to carry that history further.
It is also true that
the period from prehistory
to Newton
(i.e.,
circa 1700
when Newton's work
was essentially done)
is a unity in the history of
cosmology as
yours truly argues at length below in
the section
An Essay on the Three Epochs of the History of Astronomy: Not a Required Reading.
After Newton
is another distinct epoch in the
history of cosmology in the opinion of yours truly.
Also astronomy
becomes distinctly more than just
cosmology after
Newton.
Various fields of
astronomy become subjects in themselves.
So the history of astronomy
after Newton CANNOT be
said to be essentially just the history of
cosmology.
The era in the history of
cosmology from
Newton
(circa 1700)
to circa 1900
and current era starting circa 1900
that leads to today's cosmology
are covered briefly in
IAL 26: The Discovery of Galaxies
and
IAL 30: Cosmology---after we have
learnt enough
modern astronomy
to understand the history of those eras.
Now having rationales---at least
rationalizations---let's get on with
it---the history of astronomy to
Newton.
Some useful general references for the
history of astronomy
and the history of science
in general are:
php require("/home/jeffery/public_html/astro/mechanics/harmonic_oscillator.html");?>
php require("/home/jeffery/public_html/astro/cosmol/infinity_eternity.html");?>
Modern cosmologists usually
do NOT address "meaning of", but it seems to hover NOT far away from their expessed concerns.
And it seems reasonable that if we ever fully understood
universe on the largest scales,
that understanding would have implications for "meaning of"---but it's hard to say what
those implications will be.
php require("/home/jeffery/public_html/astro/newton/newton_principia.html");?>
But why stop in particular with the age of Newton?
Second, yours truly is knowledgeable about the subject, but NOT a great expert. Yours truly has NOT done relentless checking of aspects---caveat lector.
Third, it is mainly the history of astronomy in the cultural region western Eurasia---and counting North Africa as part of western Eurasia as culturally it is---for two reasons:
Other astronomical traditions (e.g., Chinese astronomy, Indian astronomy, Mayan astronomy) have their interest in the general history of science and the history of culture, but just arn't as interesting qua astronomy in the opinion of yours truly.
We will be unabashedly western-Eurasia-ocentric.
Astronomy
is often cited as the oldest, empirical, exact science.
There is lots of reasoning including
a priori reasoning
in empirical sciences too, of course.
And what of the relationship to physics?
One can say that astronomy pre-dates
empirical, exact physics and then was absorbed by it.
Or one could say that astronomy
was the original empirical, exact physics.
Yours truly favors the latter view.
In very simple ways, probably way back in
the Paleolithic (2.6 Myr ago to circa 8000 BCE)
when humankind first developed
a sufficiently sophisticated language---but exactly
when that was we do NOT know
(see Wikipedia: Origin of language).
See the Paleolithic (2.6 Myr ago to circa 8000 BCE)
(i.e., the good old days) illustrated in
the figure below
(local link /
general link: pleistocene_mammoth.html).
There were calendrical reasons,
but these need only very modest
input from astronomy:
Of course, the farther you go from the equator,
the more obvious the astronomical seasons:
the changing length of
daylight/nighttime
and
changing position of the Sun relative to the
horizon during the course of
the day.
Of course also, the farther you go from the equator,
more obvious the seasons are
as observed
primarily from weather and the
behavior of
biota.
So the astronomical seasons are NOT
needed much calendrically even though they are obvious anyway.
There is NO reason to doubt that prehistoric and early historic
(i.e., literate) peoples saw celestial phenomena as
signs from
gods---particularly
rare phenomena that were unpredictable (or seemingly so)
like comets,
eclipses,
and
bolides
(much brighter than usual meteors).
The rare phenomena were usually probably thought of as being
signs aimed at all and/or
at rulers
portending
great disasters (meaning something like
destroying stars).
But, of course, prehistoric and early historic peoples
mostly just saw
the sky as part of
everyday life---it's
just there, part of the background.
Yours truly
has NEVER heard of anyone directly worshiping
celestial phenomena, but rather they regarded these phenomena as established by
the gods
or taking place in the realm of the gods.
The idea of making a systematic
theology of their beliefs
probably seldom occurred to them.
In most cases, their gods
were anthropomorphic gods
at least psychologically if NOT always in form.
Anubis straddles the line in form as
shown in the figure below
(local link /
general link: anubis.html).
However, they did NOT regard
those particular astro-bodies
as being the only
manifestations of those
particular gods.
They seemed to have principally thought their
gods were manifested by divine images
maintained in temples
(see Op-???;
Wikipedia: Babylonian religion:
Importance of idols).
Dante Alighieri (1265--1321)
gives the famous retelling of the concept
that the observed Heavens were the
theological Heaven in his
Divine Comedy.
See the figure below
(local link /
general link: dante_beatrice.html).
See more
Divine Comedy.
in the figure below
(local link /
general link: dante_divine_comedy.html).
In any case, Medieval Christianity
did NOT include sky worship.
But they were particularly conscious of
signs
from the
gods.
The behavior of birds and the entrails of sacrificial animals
(i.e., haruspicy)
were particularly
popular regions to look for such
signs
at least in the
Mediterranean region
and
Mideast.
But celestial
signs have always had particular resonance and there
is a tradition that they were aimed primarily at
royalty and
rulers.
Comets, in particular, were
often considered ominous.
See the great image of
Comet Lovejoy
in the figure below
(local link /
general link: comet_lovejoy.html).
With (horoscopic) astrology---invented
by Babylonian astronomers---astro-divination
became democratized:
the stars
at least partially determined everyone's character and at least influenced their activities.
Astrology tended to become understood as a science based
on regular cause/influence and effect/tendency and less as direct messages from the
gods.
See the consulting
astrologer at work in the
figure below
(local link /
general link: astrologer.html).
Most naked-eye
celestial events are regular, but they come in a multitude of combinations.
Thus, astrology
could develop a vast realm of possible influences based on particular combinations for
imaginative astrologers to work with.
The influences are often easy to identify---Venus in your
astrological sign
is NOT hard to read---but giving the influences their exact weight is
where the art of the astrologer was needed.
Direct
signs
from the Heavens
were still believed in, of course.
Irregular events like comets were considered particularly ominous.
Some like Johannes Kepler (1571--1630)
did try to make it scientific, but they failed because there is nothing to it.
Of course, astrology still works.
It usually gives you positive advice and positive advice is usually good, and so
if you follow your horoscope, your day
will usually be better.
But the same is true if you follow your
mother's advice.
There have always been dissidents,
of course:
Think of Oedipus
and The Mayor of Casterbridge (1886)---and,
of course,
Brutus (85--42 BCE):
see the figure below
(local link /
general link: brutus_caesar_ghost.html).
php require("/home/jeffery/public_html/astro/art/art_m/muse_astronomy_2.html");?>
And now on with the show:
"Empirical" meaning based on observation, NOT purely
a priori reasoning.
One can quibble, but there really is no other candidate for oldest empirical
exact science if one regards
mathematics
as an abstract science that is only applied in the physical world.
In fact, the terms
astronomer
and mathematician
up to circa 1800
(and astrologer too up to
circa 1630)
were often regarded as near synonyms.
This is because the most
advanced math was usually
in the service of mathematical astronomy
(as well as in other services also)
up until circa 1800, and so leading
mathematicians were often
leading mathematical astronomers too.
How old is astronomy as an empirical, exact science?
php require("/home/jeffery/public_html/astro/art/art_p/pleistocene_mammoth.html");?>
In fact, it seems very likely that the
days of the
lunar month
were counted as far back as people did
counting
and those counts
would have been kept track of by some means
in many Paleolithic societies
for calendrical reasons.
For more pondering on
astronomy
as the oldest
empirical
exact science, see the figure below
(local link /
general link: sapien_neanderthal.html).
php require("/home/jeffery/public_html/astro/archaeoastronomy/sapien_neanderthal.html");?>
The lunar month and
lunar phases are illustrated in the
animation in the figure below
(local link /
general link: moon_lunar_phases_animation_2b.html).
php require("/home/jeffery/public_html/astro/moon/moon_lunar_phases_animation_2b.html");?>
To conclude,
plausibly exact astronomy---in a very modest sense---goes
back tens of thousands of years.
Hunter-gatherers
and early agriculturalists
probably didn't need more for calendars
than the day-night sequence, the lunar phases
and seasons as observed
primarily from weather and the
behavior of
biota and
NOT primarily astronomically.
However, even from its earliest days, some observers were probably interested in
astronomy for its own sake.
They wanted to know where things in the sky
were and when they would appear.
Every human activity can become an end in itself---this explains, for example,
stamp collecting
(AKA Philately)
(see the figure below
local link /
general link: stamp_collector.html)
trainspotting,
and ship watching---which
as Orhan Pamuk (1952--)
tells us in
Istanbul: Memories and the City
(2005) goes on all the time in
Istanbul.
php require("/home/jeffery/public_html/astro/art/art_s/stamp_collector.html");?>
But astronomy for
astronomy's sake was
probably NOT important for most early people.
It has to be emphasized that early religions usually had NO definite
formulation of theology NOR fixed dogma.
So it was perfectly possible, for example, for an adherent
to believe the
Moon in the
sky
was the
Moon god
and at the same time believe the
Moon god
was person who you could talk to.
php require("/home/jeffery/public_html/astro/art/art_a/anubis.html");?>
The ancient Babylonians
for example certainly took a keen religious
interest in
astronomy
and believed the Heavens
were under the power
of their
gods
and that
particular astro-bodies
were manifestations of particular gods.
Their religious observances were certainly centered on the temples, NOT
on the celestial phenomena.
On the other hand,
Medieval Christianity
certainly had a TENDENCY,
reinforced by Aristotelianism,
to regard the observed Heavens as part of the
theological Heaven---the
realm of
God and
angels.
But this concept was NEVER seen as an
article of faith.
But it must be emphasized that Dante
was consciously writing an allegory
and referred
to aspects of his story as "the fable"???.
php require("/home/jeffery/public_html/astro/art/art_d/dante_divine_comedy.html");?>
To conclude, it seems
that early peoples probably did NOT worship the sky in any direct sense.
php require("/home/jeffery/public_html/astro/comet/comet_lovejoy.html");?>
php require("/home/jeffery/public_html/astro/art/art_a/astrologer.html");?>
How does astrology work?
It goes without saying that
astrology is
totally a pseudoscience nowadays
and usually it was that in the past too.
Astrology
is still with us: it's only a click away
to your horoscope.
When astrologers meet, no speech,
As well as
Cicero (106--43 BCE),
there was also
Cassius (before 85--42 BCE)
among the dissidents:
see the figure below
(local link /
general link: brutus_james_mason.html).
but they smile each to each.
---Cicero (106--43 BCE),
misquoted from memory
or yours truly just made it up---one or the other.
php require("/home/jeffery/public_html/astro/art/art_b/brutus_james_mason.html");?>
But dissidents usually come to a sticky end:
If you realize you are a fictional character
and the
foreshadowing is against you,
then you might as well throw
in the towel---the author is out to get you.
You can squirm, but the
author will just turn that into bitter
irony.
php require("/home/jeffery/public_html/astro/art/art_b/brutus_caesar_ghost.html");?>
php require("/home/jeffery/public_html/astro/archaeoastronomy/newgrange_1905_3.html");?>
But the prehistoric astronomy that we know most about is simple alignment astronomy using the horizon as a natural measurement tool. We take this subject up in the subsections below.
Note: Archaeoastronomy is the study of prehistoric and early-literate astronomy in its cultural role. In this lecture, we cross over the line into archaeoastronomy sometimes. An example of an object of archaeoastronomy is Newgrange (built c.3200 BCE): see the figure below (local link / general link: newgrange_1905.html). We discuss Newgrange (built c.3200 BCE) below in subsection Newgrange in Ireland.
Prehistoric peoples,
and ancient historistoric peoples,
were keenly aware of
horizon phenomena
(rising and settings of bright stars,
etc.)
because the horizon provides
a natural measurement tool.
We can consider one important example
of a horizon phenomenon
heliacal risings (of stars).
Important to
prehistoric peoples,
and ancient historistoric peoples
that is---us NOT so much.
The heliacal risings
of commonly recognized
bright stars
mark the times of
solar year = 365.2421897 days (J2000).
So you could tell whether it was
January,
February,
March,
etc.
(by whatever name you used)
by recognized heliacal risings
But, of course, you could do that by weather too.
Heliacal risings
are explicated in the figure below
(local link /
general link: heliacal_rising.html).
Elaborating on just casually observing
horizon phenomena is
alignment astronomy:
finding the alignments for the
rising and setting of astronomical objects.
How did early peoples do
alignment astronomy?
They made observations using natural
horizons or simple artificial
horizons (e.g.,
sticks in the ground).
The procedure is illustrated in the figure below
(local link /
general link: horizon_observation.html).
Remember the Earth is a point compared to the
celestial sphere.
So any astronomical object on the
celestial equator will be on a plane
that is perpendicular to the
celestial axis
(which is also the
Earth's axis)
and that includes the point Earth.
So astronomical objects
on the celestial equator
can only rise due east
and can only set due west.
If an astronomical object
is rising in the east, but
is NOT on the celestial equator,
it will be north or south of due east.
The relationship of the
due east-due west line
and the perpendicular
due north-due south line
is made clear in the figure below
(local link /
general link: sunpath_equinox.html).
Alignment astronomy
is very easy to do---it's NOT
rocket science.
Simple artificial horizons
are easy to build too---a few stakes in the ground or a few stones.
But many
prehistoric peoples
and early historic peoples
built very elaborate artificial horizons
or other structures embodying their astronomical lore.
These structures
can be justly called
astronomical monuments.
By definition, prehistoric people
were illiterate, and so they didn't write anything down.
The astronomical monuments
are their records of their astronomical knowledge.
The study of such
astronomical monuments
is a main part of
archaeoastronomy
and archaeology too.
The most famous
astronomical monument
is
Stonehenge.
But there are many other
astronomical monuments
or possible ones from
prehistoric cultures
and early historic societies all over the world.
We consider some famous
astronomical monuments
(including possible ones)
in the subsections below.
Where is Stonehenge?
See the physical map
of the Hiberno-British Isles
in the figure below
(local link /
general link: map_british_isles_physical.html).
It's a circular structure of
megaliths which are large stones
used in structures.
See the figures below
(local link /
general link: sullivan_stonehenge_001_far_off.html;
local link /
general link: sullivan_stonehenge_002_whole.html;
local link /
general link: sullivan_stonehenge_003_remains.html).
The most certain intentional alignment is set by the
Heelstone.
Caption: Sunrise over the
Heelstone at
Stonehenge
at the summer solstice.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Caption: "The Sun
rising over Stonehenge on the morning of the
summer solstice
(2005 Jun21)."
There are actually hordes of people there---you can see their
silhouettes.
Credit/Permission: ©
Andrew Dunn (AKA User:Solipsist),
2005 /
Creative Commons
CC BY-SA 2.0.
There are other possible astro alignments at
Stonehenge that can be found
when viewing the horizon from the Altar Stone
(see Wikipedia: Archaeoastronomy and Stonehenge).
But we won't go into them.
More extravagant claims of astronomical functions
for Stonehenge
are certainly false:
e.g., that Stonehenge was an analog computer used to calculate
eclipses (see Wikipedia:
Archaeoastronomy and Stonehenge: Gerald Hawkins's work).
They demonstrate the ingenuity of posterity.
For more thrills, see
Stonehenge videos
below
(local link /
general link: stonehenge_videos.html).
The
Great Serpent Mound is a
Native American
structure
in Adams County, Ohio.
See the figure below
(local link /
general link: great_serpent_mound.html).
The Giza Pyramids are
the tombs
of the pharaohs
of the 4th Dynasty
of the Old Kingdom of
ancient Egypt.
See the figure below
(local link /
general link: giza_pyramids.html).
Newgrange
is a Neolithic structure in
County Meath,
Ireland.
See the figure below
(local link /
general link: newgrange_1905.html).
El Caracol, Chichen Itza
is a likely
astronomical monument
of ancient Mayan astronomy:
see the figure below.
(local link: File:Chichen Itza 4.jpg)
Note Chichen Itza is
an ancient Mayan
city in the
Yucatan state of
Mexico.
Caption: El Caracol, Chichen Itza
(constructed circa 906 CE)
is a likely
astronomical monument
of ancient Mayan astronomy.
Chichen Itza is an
ancient Mayan
city in the
Yucatan state of
Mexico.
Chichen Itza is believed to have
flourished in the period circa
750--1250
(see Wikipedia: Chichen Itza: History).
El Caracol
is NOT only considered
to be a likely
astronomical monument,
but also an actual likely
observatory: i.e., a
building for gathering
new astronomical data.
The tower
(whose original shape was a smaller cylinder on top of a larger one) is conjectured to have
allowed Mayan astronomers
to view the sky well above the
vegetation which blocked much of the view of the
sky.
In particular, the tower would have allowed
Mayan astronomers
to see horizon phenomena
(risings and settings) better.
Horizon phenomena
were often considered very important in early
astronomy.
The possibility that
El Caracol was
an observatory, even in a very elementary
way, distinguishes it from most
astronomical monuments
which were almost certainly just records of astronomical knowledge as well as serving
other probably much more important cultural functions, and NOT
observatories.
For more information on El Caracol, Chichen Itza,
see
Echoes of the Ancient Skies: The Astronomy of Lost Civilizations (1983), p. 52--58 by
Edwin C. Krupp (1944--).
Credit/Permission: ©
Daniel Schwen (AKA User:Dschwen),
2009 /
CC BY-SA 4.0.
It must be absolutely emphasized that
Stonehenge
and ALMOST ALL the other prehistoric and early
astronomical monuments
embodying astronomical lore were almost certainly NOT
observatories: i.e.,
buildings for gathering
new astronomical data.
They probably embodied astronomical lore discovered by simpler artificial horizons---stakes
and stones.
They were monuments
recording the astronomical lore---for illiterate peoples, there
was no other way of recording it.
A prime possible example is
El Caracol, Chichen Itza which is
is discussed in the figure above
(local link: File:Chichen Itza 4.jpg).
And it also must be absolutely emphasized that the
monuments
were probably in most cases NOT primarily for
recording astronomical lore.
The monuments
embodying
alignment astronomy
probably in most cases (including Stonehenge)
had multiple uses and significances.
Their astronomical use/significance was probably only one among many uses/significances.
Stonehenge, for example, was obviously
a cult center with religious and cultural meanings that only included astronomical ones among others
(see Wikipedia: Stonehenge:
Function and construction).
In fact, people attended religious and cultural
ceremonies at Stonehenge
and may have gone there for trade and holidays too.
For Stonehenge
in use in modern times, see the figure below
(local link /
general link: stonehenge_neo_druids.html).
In later ages, when astronomy
become much more developed, incorporating
astronomy lore into buildings
for recording or symbolic reasons
declined it seems, except for some simple cases: e.g.,
cathedrals are often
aligned approximately west-to-east so that worshippers face approximately the rising
Sun
(see Wikipedia:
Cathedral: Symbolic functions of the building).
In the modern age, incorporating astronomy
lore into buildings is rare,
but it is occasionally done for ornamentation
such as for the UNLV's Bigelow Physics Building
(see
Physics Building Dedication, 1994)
and, more prominently,
Grand Central Station:
see the figure below.
Caption: The
astronomical ceiling
of Grand Central Station,
New York City.
Clearly seen are the zodiac constellations
along the ecliptic,
the celestial equator,
Orion,
Pegasus,
the Milky Way,
and lots of stars---and
the Stars and Stripes.
The astronomical ceiling
is NOT an accurate
sky map though some parts are correct.
One obvious error is that
Orion has a reversed orientation
relative to Taurus.
The Wikipedia does NOT say if the
astronomical ceiling
aligns with the sky
as seen from the
latitude of
New York.
The astronomical ceiling
was designed 1912 by
architect
Charles Warren (1866-1941)
with his friend
artist
Paul Cesar Helleu (1859--1927)
(see Wikipedia:
Grand Central Terminal: Ceiling).
Their intention was probably ornamentation plus a bit of
science
frisson.
Unlike the
monuments
of archaeoastronomy,
the astronomical ceiling has
no deep cultural significance, except the very general one that modern society is
a science based society---and except that we still
do astrology for fun.
The mistakes in the
astronomical ceiling
are probably due to an inaccurate reading by the designers of a
sky map sketch provided by
Harold Jacoby (1865--1932),
astronomy professor at Columbia University,
New York City.
Grand Central Station
(official name Grand Central Terminal)
was built in the period
1903-1913
(see Wikipedia:
Grand Central Terminal: Grand Central Terminal)
It is a famous landmark of
New York and is often used
in establshing shots---"We are now in
New York."---and it turns up in
literature: e.g.,
By Grand Central Station
I Sat Down and Wept (1945)
by Eizabeth Smart (1913--1986).
Credit/Permission: ©
User:Arnoldius,
2008 /
Creative Commons
CC BY-SA 3.0.
Astronomy
lore is also sometimes incorporated into buildings
for historical/cultural/educational/fun reasons such as for
Stonehenge replicas:
see the figure below
(local link /
general link: stonehenge_carhenge.html).
As mentioned in the Introduction,
there may well have been a few individuals with some purely astronomical interest, but
probably that was NOT the main interest of early peoples.
There were calendrical reasons as we also mentioned in the
Introduction, but these need only very modest
input from astronomy:
Caption: A country lane in England
in fall.
You know the season from the
fall colors and the
fallen leaves.
You do NOT have to check for the
fall equinox.
Credit/Permission: User:Jongleur100,
2008 /
Public domain.
But more elaborated societies have
terms of office, contracts with termination dates,
and religious observances/events all of which are thought to require exact times.
Such societies needed elaborate calendars depending
on the natural astronomical clocks provided by the astronomical cycles of the
Sun,
Moon,
planets,
and
fixed stars
(e.g., via their heliacal risings).
Those natural astronomical clocks were considered to measure true time---which
they do to high, but NOT perfect, accuracy in our modern physics view.
However, in traditional societies, the
rather obscure natural astronomical clocks
of highly detailed astronomy
were well beyond calendrical needs for civil purposes
and were probably mainly for cultural and astrological purposes, and
eventually horoscopic astrology.
We know this was true for the
ancient Babylonians
and can assume it confidently for other early societies including that of the
Stonehengers (AKA Neolithic Britons).
Remember time flows at different rates
in different reference frames
as per
the theory of relativity.
For the observable universe
within the theory
of Big Bang cosmology, there
is cosmic time
which counts off the expansion of the universe.
Cosmic time is probably our
our best choice in principle
for true time, and we can measure its passing to some
accuracy/precision.
However, the rate of flow of time on
Earth
(which super closely approximates that of the
free-fall frame of the
Solar-System barycenter)
can be measured very
accurately with atomic clocks.
The local time
of the free-fall frame of the
Solar-System barycenter
is what the
Solar System evolves with respect to,
and so is our best local true time.
The natural astronomical clocks
approximate this local true time
well enough for pre-1900 societies,
but NOT for modern scientific purposes and modern
metrology.
Form groups of 2 or 3---NOT more---and tackle
Homework 4
problems 2--5 on the history of astronomy
and pre-historic astronomy.
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/archaeoastronomy/newgrange_1905_2b.html");?>
php require("/home/jeffery/public_html/astro/archaeoastronomy/heliacal_rising.html");?>
The heliacal rising of
Sirius is particularly noteworthy---see
the figure below
(local link /
general link: hesiod.html).
php require("/home/jeffery/public_html/astro/ancient_astronomy/hesiod.html");?>
php require("/home/jeffery/public_html/astro/archaeoastronomy/horizon_observation.html");?>
Question: Where on the celestial sphere
is a body that rises due east?
The answer is 3.
php require("/home/jeffery/public_html/astro/celestial_sphere/sunpath_equinox.html");?>
php require("/home/jeffery/public_html/astro/maps/map_british_isles_physical.html");?>
What is Stonehenge?
php require("/home/jeffery/public_html/astro/stonehenge/sullivan_stonehenge_001_far_off.html");?>
php require("/home/jeffery/public_html/astro/stonehenge/sullivan_stonehenge_002_whole.html");?>
php require("/home/jeffery/public_html/astro/stonehenge/sullivan_stonehenge_003_remains.html");?>
A particular Stonehenge
megalith
of interest is the Heelstone:
see the figure below
(local link /
general link: sullivan_stonehenge_004_heelstone.html).
php require("/home/jeffery/public_html/astro/stonehenge/sullivan_stonehenge_004_heelstone.html");?>
Some of the geology
and history
of Stonehenge
is given in
the figure below
(local link /
general link: stonehenge_map_modern.html).
php require("/home/jeffery/public_html/astro/stonehenge/stonehenge_map_modern.html");?>
For the
alignment astronomy,
(probable and unlikely both), embodied in
Stonehenge,
see the Stonehenge map
in the figure below
(local link /
general link: stonehenge_map_refined.html).
php require("/home/jeffery/public_html/astro/stonehenge/stonehenge_map_refined.html");?>
Below are two figures
illustrating the Heelstone
and the Sun
rising over Stonehenge on the morning of the
summer solstice.
Image link: Wikipedia:
File:Summer Solstice Sunrise over Stonehenge 2005.jpg.
php require("/home/jeffery/public_html/astro/stonehenge/stonehenge_videos.html");?>
EOF
php require("/home/jeffery/public_html/astro/archaeoastronomy/great_serpent_mound.html");?>
php require("/home/jeffery/public_html/astro/archaeoastronomy/giza_pyramids.html");?>
php require("/home/jeffery/public_html/astro/archaeoastronomy/newgrange_1905.html");?>
Image link: Wikimedia Commons:
File:Chichen Itza 4.jpg.
Local file: local link: File:Chichen Itza 4.jpg.
There may be a few
astronomical monuments
that were observatories in an elementary way.
php require("/home/jeffery/public_html/astro/stonehenge/stonehenge_neo_druids.html");?>
Image link: Wikipedia:
File:NYC Grand Central Terminal ceiling.jpg.
php require("/home/jeffery/public_html/astro/stonehenge/stonehenge_carhenge.html");?>
Of course, buildings ancient and modern often embody solar
astronomical science for the practical reasons of lighting and/or heating
(see Wikipedia: Passive solar building design).
Hunter-gatherers
and early agriculturalists
probably didn't need more for calendars
than the day-night sequence, the lunar phases
and the seasons as observed a bit from
astronomy, but more obviously from
weather and the
behavior of
biota: see
fall
biota behavior in
the figure below.
They noticed the
astronomical seasons too, of course.
Image link: Wikipedia:
File:Country lane.jpg.
By the by, what is true time?
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_3.html");?>
Group Activity:
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
The ancient Mesopotamians developed one of the world's first two literate civilizations in what is now Iraq and what historians call Mesopotamia.
In the early literate phase circa 3000---2000 BCE, the region was called Sumer and we call the people Sumerians.
After circa 1800 BCE,
Babylon became the
principle city of Mesopotamia.
Because of this fact,
we moderns tend to call the
southern part of Mesopotamia
Babylonia
after circa 1800 BCE
until its culture and political nature gradually
got rather thoroughly transformed in the
1st millennium CE
(see Wikipedia: Babylonia: Persian_Babylonia).
See the map of
Babylonia in the figure below.
Caption: A Mercator projection
map
(with north at the top)
of Babylonia in the
time of king
Hammurabi (reigned c. 1792--1750 BCE, middle chronology).
The rivers
and coastline
are for Hammurabi's epoch.
The map is a historical reconstruction,
and so has some uncertainties.
The cities have their special places in
history
and legend:
Hammurabi is known for his
Code of Hammurabi,
one of earliest known
law codes.
It's nothing like
The Code of the Woosters (1938).
Credit/Permission: ©
User:MapMaster,
2008 /
Creative Commons
CC BY-SA 3.0.
Below are two figures
of Babylon the great.
Caption: Babylon in
1932
long before
the reconstruction
started by Saddam Hussein (1937--2006)
in 1983.
The reconstruction
is controversial since it probably seals off and damages archaeological artifacts.
Credit/Permission:
Anonymous photographer,
1932
(uploaded to Wikipedia
by User:Jake73,
2007) /
Public domain.
Caption: "Babylon,
Iraq,
(2005 Mar21.
U.S. Army Soldiers
assigned to the 155th Brigade Combat Team (BCT),
are given a tour of the historical city of Babylon
as a gesture of goodwill by the Iraqi people
in Babil,
Iraq.
These periodic tours of the ancient
ruins are given to service members to learn
more about Iraq's
history and help boost morale. U.S. Military Reserve and Active Duty personnel
are forward deployed to central Iraq
in support of
Operation Iraqi Freedom (OIF).
This is a digital
composite of thirteen images to produce a 180-degree panoramic view of
Babylon.
U.S. Navy photo by Chief Photographer's Mate
Edward G. Martens (released)."
(Slightly edited.)
Like the armies of
Cyrus and
Alexander.
The ruins are NOT
real ruins because of the
reconstruction
started by Saddam Hussein (1937--2006)
in 1983.
Credit/Permission: Edward G. Martens,
US Federal Government,
2005
(uploaded to Wikipedia
by User:Petrusbarbygere,
2005) /
Public domain.
The science and
astronomy of
Babylonia written in
cuneiform script (see below)
tends to be called
Babylonian too
after 1800 BCE
until cuneiform
faded from history in the course of the
2nd century CE
(see Wikipedia: Cuneiform).
The Sumerians and
Babylonians
developed novel mathematical and astronomical techniques.
The Babylonian astronomers,
in fact, developed a sophisticated predictive
mathematical astronomy
far in advance of the simple
alignment astronomy
of earlier civilizations.
What is mathematical astronomy
and why does anyone do it?
Mathematical astronomy predicts where
astro-bodies
will be on the
celestial sphere
on given dates and related phenomena such as
conjunctions,
oppositions,
and eclipses.
The predictions are written up in tables called
ephemerides
(singular ephemeris).
See an example ephemeris
from
Medieval Islamic astronomy
in the figure below
(local link /
general link: al_khwarizmi.html).
Later horoscopic astrology
required mathematical astronomy.
The astrologer NOT only has to know that
Heavens said yesterday, but what they
will say tomorrow.
Modern astronomy
largely descended from this beginning.
Independent traditions of
mathematical astronomy
were developed by, e.g.,
Chinese astronomers
and Mayan astronomers.
Although these traditions contributed relatively little to
modern astronomy
in a direct sense, they are significant demonstrations of intellectual prowess.
They Wrote on Clay (1938, Edward Chiera, 1885--1933).
The cuneiform script
used by the ancient Mesopotamians
was written on
clay tablets.
Fired clay tablets
stored in dry conditions are
highly
non-volatile memory---they
last millennia---our
disk storage won't
last as long---when archaeologists
excavate our lost civilization, our disks will NOT readable.
See an example of a modern
clay tablet made
by ancient means in the figure below
(local link /
general link: cylinder_seal.html).
Many of the clay tablets
are inventories and tax records---they are still being
audited.
There is some
Babylonian literature like
Epic of Gilgamesh:
see the figure below
(local link /
general link: gilgamesh.html).
These are mostly calculations, observations,
and ephemerides.
There is virtually no records of astronomical theories.
There is some
Mesopotamian mythology
which contains astronomy lore---but that's NOT science.
See the figure below
(local link /
general link: sumerian_gods_tablet.html).
For example, we know a fair amount about
Babylonian mathematics
and the Babylonian sexagesimal system.
The
Babylonian mathematicians
(and their predecessors
in ancient Mesopotamia
the Sumerian
mathematician)
used a sexagesimal system
(i.e., base-60 system) for
mathematics and
astronomy.
One can convert thusly "11"=1*60+1=61.
After that, we turn to
Babylonian astronomy.
Caption: An animation giving
a visual proof of the
Pythagorean theorem.
Proof explicated:
The visual proof is NOT complete.
One actually has to assume that
one has a 2-dimensional
Euclidean space
with the properties of such a space.
For further explication, see, e.g.,
Roger Penrose, The Road to Reality, 2004,
p. 25--33).
Credit/Permission: ©
John Blackburne (AKA User:JohnBlackburne),
2010 /
Creative Commons
CC BY-SA 3.0.
The predictive
mathematical astronomy
of the
Babylonian astronomers
had simple beginnings in using cycles of repeated astronomical motions.
Early evidence of this is the
Venus Tablet of Ammisaduqa:
see the figure below
(local link /
general link: venus_tablet.html).
You can build up cycles for the other planets and
for eclipses.
For example, all eclipse phenomena repeat approximately about every 18 years:
this is called the Saros cycle
by moderns.
The Saros cycle is discussed in
a bit more detail in
IAL 3: The Moon: Orbit, Phases, Eclipses, and More.
We can see that a primitive mathematical astronomy
can be built up from cycles.
The Babylonian astronomers did this first.
But they advanced.
In the period
400 BCE--100 CE,
Babylonian astronomers
reached their highest level.
Some of their most notable achievements:
The
ancient Greek astronomers
Timocharis (c.320--c.260 BCE)
and Aristillus (fl. 260 BCE)
introduced the arcminute
in Classical Antiquity
(see
Wikipedia: Hipparchus: Babylonian sources).
The
arcsecond
may have been too small an angular unit for the
Ancients
to have bothered with.
They could NOT measure to that accuracy to anything close to
arcsecond
accuracy
Ptolemy (c.100--c.170 CE)
via his treatise the Almagest
passed the arcminute to posterity???.
Ephemeris is a singular
which is hard to remember.
Ephemerides is the plural
ephemeris which is also hard to remember.
There clearly was a cycle of
theory and observation leading to better and better predictive
results and a deeper knowledge of mathematical technique---the
scientific method was practiced.
In fact, we don't know that much about what
the Babylonian astronomers
thought about astronomy.
Our understanding of their mathematical astronomy
just comes
from observational,
calculational and ephemeris
clay tablets.
All we know is that the astronomy tablets were written in a clerical environment it seems
We have no/little evidence that there was any Babylonian
astrophysics:
i.e., an attempt to understand the celestial motions in terms of some physical laws.
Also there are only traces of any
scientific Babylonian cosmology.
Even the
Wikipedia section
on Babylonian cosmology
fails to convey much of anything
(see
Wikipedia: Babylonian astronomy: Babylonian cosmology).
There was
a Babylonian mythological cosmology,
but that is another subject.
The Babylonian astronomers
may well have been satisfied with a DOME MODEL of
the cosmos in which the
astronomical objects were manifestations
of the
gods.
The figure below
(local link /
general link: babylonian_cosmos.html)
illustrates a possible DOME MODEL.
The category of DOME MODELS
is a modern catchall
category for some mythical cosmologies
that could also be considered
philosophical cosmologies.
The category that can only be vaguely specified since
various peoples at various times had various ideas that were probably often vague.
But one can say that a DOME MODEL probably
posits a flat Earth
and posits that the astro-bodies
travel
over the sky dome-like surface and then
under the Earth's surface from their setting
to their rising positions.
Under Earth's surface may in some
cases have been regarded as the underworld or
land of the dead.
See the DOME MODEL
of Norse mythology
in the figure below
(local link /
general link: cosmos_norse_yggdrasil.html).
Why did the ancient Babylonians
do astronomy?
Almost certainly the main reasons were for religious and astrological purposes.
The astronomical tablets were written in a clerical environment it seems.
Purely calendrical reasons for astronomy
also existed.
But the astronomy needed for the
calendar is far less than the elaborate
astronomy developed by
the Babylonian astronomers.
A few people may have been interested in
astronomy for its own sake---as we have
mentioned before.
But we know nothing about them.
Before going on we should mention that Babylonian exact sciences
had only two golden ages:
(1) circa 1800 --
circa 1600 BCE
in pure math
(Ne-30);
(2) circa 400 BCE --
circa 100 CE
in mathematical astronomy.
There were long stretches of time in a literate culture that
spanned from circa
3000 BCE to circa
200 CE in which
NOT much development happened---periods of stagnation.
The pattern of golden age
and stagnation seems to be typical of
science in traditional societies.
Traditional Chinese and Indian societies probably
a few golden ages---but yours truly
is NOT so well informed on these societies.
Part of the explanation
for the pattern of golden ages
and stagnations
is that science is a marginal activity
in traditional societies.
Only a few individuals practice it
and societal support, tangible and intangible, is chancy.
A few atypical individuals---well let's call them geniuses---may
feedback to each other over a few generations to create significant
progress. But the chain is broken by chance and stagnation seems
to result.
Fortunately, the achievements are usually preserved in writings and can be built on later.
Science in modern society since circa
1600
(i.e., modern science)
is radically different.
It is relentlessly progressive and strongly supported by society.
The change in the nature of science is called in historical research the
Scientific Revolution (c.1543--c.1687).
The
Scientific Revolution (c.1543--c.1687)
occurred in the 16th century and
17th century
in Europe.
See the figure below
for an illustration of the
Scientific Revolution (c.1543--c.1687)
in progress.
Caption: The frontispiece
of the
Rudolphine Tables (1627)
of Johannes Kepler (1571--1630).
It is a fitting symbol of the
Scientific Revolution (c.1543--c.1687)
of the 16th and
17th centuries.
The Temple of Astronomy.
Hipparchus (c.190--c.120 BCE),
Nicolaus Copernicus (1473--1543),
Tycho Brahe (1546--1601),
and Ptolemy (c.100--c.170 CE)
are by their pillars.
Archimedes (c.287--c.212 BCE) is NOT
with his pillar.
Maybe he's hiding behind
Hipparchus's pillar.
I can't identify the clown in the back wearing
a Phrygian cap---maybe
Pythagoras (c.570--c.495 BCE).
Kepler himself is on
metope left of center---hard
at work at his calculations.
The eagle at the top showering
gold coins symbolizes
the Holy Roman Emperor---from whom
Kepler was hopeful of getting some backpay.
Scientists are still hopeful
that emperors will
shower gold coins on them.
Credit/Permission:
Johannes Kepler (1571--1630),
Anonymous
17th century artist,
1627
(uploaded to Wikipedia by
User:Mattes,
2005) /
Public domain.
The
Scientific Revolution (c.1543--c.1687)
occurred in the 16th century and
17th century
in Europe.
Some historians of science
consider the
Scientific Revolution (c.1543--c.1687)
to be spread out over a longer time period, but even they
probably concede that the inner core of it was
in the 16th century and
17th century.
Image link: Wikipedia:
File:Hammurabi's Babylonia 1.svg.
Image link: Wikipedia:
File:Babylon, 1932.jpg.
Image link: Wikipedia:
File:The historical city of Babylon.jpg.
php require("/home/jeffery/public_html/astro/astronomer/al_khwarizmi.html");?>
Originally, mathematical astronomy
was probably mainly for calendar making, religious purposes, and
divination.
To repeat myself,
yours truly thinks there must have been some interest in
astronomy for its own sake
from the earliest times, but this was almost certainly a minority interest
until perhaps the 17th century.
It is human nature for activities to become an end in themselves.
The Babylonian astronomers
circa 1600 BCE
were probably the first to develop
mathematical astronomy beyond the level of simple
alignment astronomy.
php require("/home/jeffery/public_html/astro/babylon/cylinder_seal.html");?>
From caches of
cuneiform
clay tablets
excavated in the
Mideast,
we know a great deal about
ancient Mesopotamia.
php require("/home/jeffery/public_html/astro/art/gilgamesh.html");?>
And there are astronomical texts.
php require("/home/jeffery/public_html/astro/babylon/sumerian_gods_tablet.html");?>
From the cuneiform
clay tablets,
we actually know a great deal about how the
ancient Mesopotamians
did astronomy---just NOT what they thought about
astronomy.
Question: If "1" is used to represent
the sexagesimal system 1, what in the ordinary
decimal system is meant by "11" in
the sexagesimal system?
Babylonian mathematics
is explicated a bit in the figure below
(local link /
general link: babylonian_cosmos.html).
Answer 1 is right.
php require("/home/jeffery/public_html/astro/babylon/babylonian_math.html");?>
The animation in the figure below
gives a visual proof
of the Pythagorean theorem.
Image link: Wikipedia:
File:Pythag anim.gif.
php require("/home/jeffery/public_html/astro/babylon/venus_tablet.html");?>
The Venus Tablet
shows that the Babylonian astronomers
as early as 1600 BCE could rely on
cycles to make relatively accurate predictions.
More exactly, the Saros cycle
lasts 6585.3213 days
In mathematical astronomy, we can certainly say that
Babylonian astronomy
was scientific.
php require("/home/jeffery/public_html/astro/babylon/babylonian_360_degrees.html");?>
The 60 minutes in a hour and 60 seconds in a minute also traces back to their
sexagesimal system.
Question: What is an ephemeris?
Answer 2 is right.
php require("/home/jeffery/public_html/astro/babylon/babylonian_cosmos.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/cosmos_norse_yggdrasil.html");?>
By traditional societies, we mean in this context those without
modern science
which is all societies before about 1600
and some societies to arguably the 20th century.
The ancient Greeks
had a golden age
of science, and so did the Medieval Islamic society.
Image link: Wikipedia:
File:Libr0310.jpg.
On the topic of the
Scientific Revolution (c.1543--c.1687)
and related matters, yours truly
follows the party line of
H. Floris Cohen (1946--) and his books
The Scientific Revolution: a Historiographical Inquiry (1994)
and
How Modern Science Came into the World: Four Civilizations, One 17th-Century Breakthrough (2011).
For Floris'
Alma Mater,
see the figure below
(local link /
general link: floris_cohen.html).
Form groups of 2 or 3---NOT more---and tackle Homework 4 problems 2--7 on the early history of astronomy before ancient Greek astronomy.
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
As the map in the figure below (local link / general link: map_hellas_circa_550_BCE.html) illustrates, Ancient Greece was spread around much of the Mediterranean Basin.
php require("/home/jeffery/public_html/astro/maps/map_hellas_circa_550_BCE.html");?>
Ancient Greece
is famous in many respects.
It's well known Greek mythology as illustrated in the figure below (local link / general link: achilles_ajax.html).
php require("/home/jeffery/public_html/astro/hellas/achilles_ajax.html");?>
Among other things, it was arguably the greatest period of enlightenment in
history before the
Enlightenment.
Ancient Greece saw the beginning of western philosophy and natural philosophy, and surpassed Babylonian astronomy with Greek astronomy---which began with natural philosophy.
But that's clunky and we are stuck with the traditional terminology we have.
A timeline of significant intellectuals of Classical Antiquity is shown in the figure below (local link / general link: intellectual.html)---created on day when yours truly had too much time on yours truly's hands.
The Greek
mythical cosmology is NOT completely specified in any source.
In fact, there were probably all kinds of variations and NO definite or original version probably
ever existed.
But the primary source is the poem
Theogony by
Hesiod (circa late 8th century BCE): see
an imaginative portrait in the figure below
(local link /
general link: hesiod.html).
For societies that are geographically very localized the
dome of the sky,
underworld,
and flat Earth and
ocean seem pretty natural.
It is also natural to see the
underworld as the
land of the
dead and where
astronomical objects /
sky gods were when they were below
the horizon.
What was beyond the boundaries of the world?
One answer is:
there is a special place in Tartarus
for people who ask such questions.
But the question can't be put off forever.
A short definition of
philosophy is the study
of the reality
in terms of
first principles which
usually/always have to be discovered from their consequences.
Two main components of
philosophy have
always been
natural philosophy
(philosophy applied
to nature in the broadest sense
including human aspects)
and
ethics
(philosophy applied
to behavior of humans
or, more generally, any intelligent beings).
The philosophy
involves reason and observation/experiment.
The ancient Greek philosophers
were relatively strong on the former and pretty weak on the latter.
For
Ancient Hellas (AKA Ancient Greece) illustrated
by the Acropolis of Athens,
see the figure below
(local link /
general link: acropolis.html).
Why then and there?
There probably can be no indisputable answer, but one can try.
Ancient Greece
at that time
(i.e., Archaic Greece (circa 8th century -- 480 BCE))
was a confident society.
The confidence was probably in large measure to its success in expansion: settling colonies
around much of the
Mediterranean Basin.
For big example of an innovation, the
Archaic Greeks accepted the
alphabet
from the
Phoenicians---they
modified for the
ancient Greek language
and added vowels
(see Wikipedia:
Alphabet: Ancient Northeast African and Middle Eastern scripts)---which meant they no longer
had to say "grk".
Contact with other societies also made the
Archaic Greeks
aware that their mythology
was NOT universal---others had other
mythologies.
One can react in three ways to this information:
Probably, all reactions occurred to the
Archaic Greeks.
The case for philosophy
is pretty certain since the
Presocratic philosopher
Xenophanes (c.570--c.475 BCE) tells
us that was his reaction, more or less: his fragments:
For philosophy to flourish,
free debate is probably essential.
Their society was politically pluralistic: it was divided into many
independent city-states
(poleis: singular
polis) with
varying kinds of
government.
Very few city-states were
ancient Greek democracies,
but in most, sufficiently high-ranking
men
(but NOT women) debated political
and legal issues.
This means these high-ranking
men
(and probably others too)
could easily slide over to debating other issues
in art,
literature,
sport
(inevitably),
and, if they were so inclined,
philosophy.
It seems that given the right societal conditions some
individuals will always be interested in
philosophy
and, in particular, in natural philosophy.
In fact, in
Classical Antiquity
(AKA Greco-Roman Antiquity),
the number of people interested in
natural philosophy was
always pretty small: just few recorded persons in any
generation though
probably a much larger number of unrecorded persons of generally lesser importance.
The period of continuous progress in
ancient Greek science/nature-knowledge
(i.e.,
natural philosophy
and, speaking a bit more generally, nature-knowledge) is arguably
from circa
600 BCE to
circa 200 BCE---this was
the golden age
of ancient Greek science/nature-knowledge.
After 200 BCE,
ancient Greek science/nature-knowledge
petered out with sporadic achievements until finally extinguished
in the 6th century CE.
Why the petering out is the story for another day.
In fact, we've already covered part of it in the subsection
Golden Ages and the Scientific Revolution.
The societal situation that gave rise to the great achievements
in ancient Greek science/nature-knowledge
is similar to that of
Western Europe
in the Renaissance---a relatively
confident, open society with pluralism
and unity.
So it is NOT surprising that
the Renaissance
was, among other things, the
golden age of
Renaissance science.
The Renaissance, however, was
at a much higher scientific and technological level actually than
Classical Antiquity.
Renaissance science
did NOT, however, peter out, but accelerated into the
Scientific Revolution (c.1543--c.1687).
But that is also a story for another day.
For a large part of the story, see
H. Floris Cohen (1946--), How Modern Science Came into the World: Four Civilizations, One 17th-Century Breakthrough, 2011.
Natural philosophy
is the study of nature.
Modern science
developed from natural philosophy
and can still be considered a part of it.
However, a large part of
natural philosophy---which
yours truly will call a priori natural philosophy---is
NOT
modern science
in that it does NOT do experiments or detailed observations.
A priori natural philosophy
is largely a priori reasoning:
first principles
are assumed and the world behavior is derived from those
first principles in a vague manner with
only casual observations providing plausible and often specious validation.
To us moderns,
a priori natural philosophy
seems naive and a very weak way of studying nature---but
this is presentism.
Before the
Scientific Revolution (c.1543--c.1687)
a priori natural philosophy
seemed reasonable to people and the only path
to more than superficial knowledge of
nature.
However, the
a priori natural philosophy
could only give speculative knowledge as proven by the fact were
competing
a priori natural philosophies
that were inconsistent and that
a priori natural philosophies
are often NOT
subject to falsification.
Now there was some experimentation and---especially in
astronomy---detailed observation
before the
Scientific Revolution (c.1543--c.1687),
but the dogmatic insistence on those procedures did NOT exist then
and practitioners of
a priori natural philosophy
often regarded those procedures as just ways to superficial
nature knowledge.
See angel
of melancholia
reflecting on superficial
nature knowledge
in the figure below
(local link /
general link: melancholia.html).
For example,
natural philosophers
of
ancient Greek science/nature-knowledge
Aristotle (384--322 BCE),
Archimedes (c.287?--c.212 BCE),
Ktesibios (c.285--c222 BCE),
and
Hero of Alexandria (c.10--c.70 CE)
must have done some experimentation.
But that aspect of their work was NOT picked up by posterity.
Aristotle (384--322 BCE) (who we
discuss below in the section Aristotle)
is an especially noteworthy case.
His followers, the Aristotelians,
largely followed
Aristotle the
a priori natural philosopher,
NOT Aristotle the experimenter
in biology, his
favorite science,
Ancient astronomy is somewhat
different than other ancient
natural philosophy
since detailed accurate observations were always seen as necessary.
But in practice, the ancient
astronomers
were often sloppy with new observations being no better than the old ones.
Now
a priori natural philosophy
is NOT worthless.
It is where the study of
nature as a
science began
in Ancient Greece.
More importantly, the speculations of
a priori natural philosophy
treated, NOT as dogma, but
has hypotheses that lead to further investigations are important to
science.
One may say poetically that all
scientists
have an inner a priori natural philosopher
who they consult for wild and crazy ideas.
Let's now start our march through the glory that was
Greek astronomy.
The first
natural philosophers
were the Presocratic philosophers
of ancient Greece.
They were definitely
a priori natural philosophers in the terminology
of the last subsection.
The Presocratic philosophers
were NOT aware that they were
Presocratic since they were NOT aware that
Socrates (c.469--399 BCE) was coming along.
In fact, some of the Presocratics
were contemporaries of
Socrates and even lived until after his death: e.g.,
Democritus (c.460--c.370 BCE).
See the two figures below
(local link /
general link: presocratic_timeline.html;
local link /
general link: socrates_death.html).
The
earliest Presocratic philosophers---were from
Ionia (now western
Turkey).
See the map and image of
Ionia in the
two figures below
(local link /
general link: ionia.html;
local link /
general link: ionia_samos.html).
Thales,
Anaximander,
and
Anaximenes,
all tried to create theories
of the cosmos that were based on ELEMENTARY PRINCIPLES without
invoking anthropomorphic gods---no
Zeus,
no Hecate.
See the image of
Hecate in the figure below
(local link /
general link: hecate.html).
They were trying to understand how the world could arise out of some basic "element".
In modern times, we know the elements
and lots of sub-atomic particles too.
Pythagoras was different kind of cat.
He founded a sect,
the Pythagoreans, that believed that the
world is based on mathematics.
This belief could have led to
mathematical physics, but in fact led
to mathematical mysticism
(see Wikipedia:
Pythagoreanism: Natural philosophy)
and a sort of religion
(see Wikipedia: Pythagoreanism: The akousmatikoi).
See
imaginative Pythagoreans
in the figure below
(local link /
general link: pythagorean_sunrise.html)
The scientific ideas of the
earliest Presocratics
seem naive at first glance.
This is partially because they were naive---the earliest
Presocratics
were just starting out in
philosophy after all.
But it is also because that only fragments of their writings/arguments
have been passed down to us from
Classical Antiquity.
If we had more of their writings/arguments, their ideas might seem more cogent.
Some reconstruction of their thinking is possible
(see, e.g., David Furley (1922--2010),
The Greek Cosmologists, 1987).
The cosmological models of the
Presocratic philosophers
were largely based on reasoning from simple, crude observations, with almost NOTHING that
can be called detailed observation or experiment.
The models can be described as rational myths.
But the were very interesting in themselves and in being the origin of
physical cosmology.
We can't discuss all the cosmologies.
But we will discuss below aspects of those of greatest interest for the development of
astronomy:
the cosmologies of
the Atomists,
Parmenides (early 5th century BCE)
(the spherical Earth theory),
and
the Pythagoreans
(the Philolaic system).
After that a few more pertinent topics before moving on to
Aristotle (384--322 BCE) and
Aristotelian cosmology.
The
atomists
Leucippus (first half of 5th century BCE)
and Democritus (c.460--c.370 BCE)
invented the original concept of atoms:
atomist atoms to coin an expression.
See the imaginative portrait of
Democritus (c.460--c.370 BCE)
in the figure below
(local link /
general link: democritus.html).
The reasoning of the atomists
(as reconstructed by
David Furley (1922--2010),
The Greek Cosmologists, 1987, p. 124)
was there had to be something to give stable structures.
But all
macroscopic structures are subject
to change (are divisible).
So what is unchangeable (indivisible) must be below perception: i.e.,
microscopic.
And there is some truth as we now know to the reasoning of the
atomists.
The microscopic stability
of the world is supplied by the quantization of
quantum mechanics---every
kind of fundamental particle is an
identical particle,
every kind of composite particle
in the limit of being unperturbed is an
identical particle, etc.
The atomist atoms were absolutely
indivisible (i.e., unbreakable) and were eternal.
They had shapes that gave them their particular properties
and they moved in the
atomist void which was absolutely
empty space.
In fact, the atomists
made very little real progress in making
atomist atoms
a useful
scientific theory.
To do that you have to use
atoms in
chemistry and that did NOT
happen until John Dalton (1766--1844).
However, the modern concept of atoms
did derive from the atomist atoms.
The chain of atomic thinking is unbroken: omitting quite a few names:
Leucippus (first half of 5th century BCE),
Democritus (c.460--c.370 BCE),
Epicurus (341--271 BCE),
Lucretius (c.95--c.55 BCE),
Pierre Gassendi (1592--1655),
Walter Charleton (1619--1707),
Robert Boyle (1627--1691),
Isaac Newton (1643--1727),
John Dalton (1766--1844),
Ludwig Boltzmann (1844--1906),
J. J. Thomson (1856--1940,
Jean Baptiste Perrin (1870--1942),
Ernest Rutherford (1871--1937),
Albert Einstein (1879--1955),
Niels Bohr (1885--1962),
Erwin Schroedinger (1887--1961).
See Isaac Newton's (1643--1727)
thinking on atoms in the figure below
(local link /
general link: newton_atoms.html).
Aristotle (384--322 BCE),
by the by,
rejected atoms: there is NO smallest,
the void is a vacuous concept.
In fact, most of natural philosophy
rejected atoms until the
19th century:
they were often thought to imply atheism---a position to be avoided at all costs.
Actually,
Democritus (c.460--c.370 BCE) and
Epicurus (341--271 BCE)
did believe in gods, but thought
they didn't do anything, except maybe flit around like
ghosts
(see Fu-161).
The
cosmology of
the atomists
cosmology of the
atomists
(mostly due to
Democritus (c.460--c.370 BCE)
it seems) is impressive---but still a rational myth with only casual observations to
support it empirically.
Atomist cosmology
is explicated in the figure below
(local link /
general link: cosmology_atomist.html).
In fact, vortices are everywhere---see the figure
below
(local link /
general link: leonardo_da_vinci_deluge_creation.html).
The animation
in the figure below
(local link /
general link: sky_swirl_polaris_animation.html)
dynamically illustrates this rotation.
We now move westward to
southern Italy (which
was part of Ancient Greece) to
where lived Parmenides (early 5th century BCE).
For an example of a tourist attraction
of western Ancient Greece,
see the figure
(local link /
general link: hellenic_theatre_segesta.html).
For example, as you go farther north in the
Northern Hemisphere, there are more
circumpolar stars.
Recall in astro jargon,
altitude
is angle measured straight up from the horizon.
This is true whatever the orientation of the
Sun and Moon are
to the horizon and whatever path the Moon takes through the
umbra.
Unless the Earth were round, the roundness of its shadow would
be hard to arrange.
(By the way, you had to believe that lunar eclipses were caused
by the Earth's shadow for this idea to be valid.)
This argument was presented by
Aristotle (384--322 BCE)
without claiming originality
(see Wikipedia:
Spherical Earth: Classical Greece).
The sinking-below-the-horizon argument was presented by
Strabo (64/63 BCE--c.24 CE)
without claiming originality
(see Wikipedia:
Spherical Earth: Roman Empire).
With the spherical Earth theory
progress was possible in cosmology.
The nature of the Earth
would NOT be considered part of modern cosmology.
It's much too small.
But historically, the
Earth,
Moon,
Sun, and
the planets of the
Solar System
were key elements of the cosmos
as it was understood.
The fixed stars was
soon thought to be larger, but NOT much larger.
Nothing was known galaxies at all---except that
Milky Way was a dim white band on the
night sky.
It is also necessary to point out that
modern cosmology
would NOT have been possible without having solved the
"Solar-System
cosmology"
(planet theory)
of the Ancients---which they
never did solve.
The Ancients
had a major problem in
"Solar-System
cosmology"
(AKA planet theory) which had been around since forever and would only start to be
solved in the 17th century.
The distance problem. See the figure below
(local link /
general link: distance_problem.html).
In the subsections below and the next two sections
(i.e., sections Aristotle and
Mathematical Ancient Greek Astronomy)
we will see how far the
ancient Greek astronomers got
in "Solar-System
cosmology" without
a solution to the distance problem.
In the 5th century BCE,
the first planetary model of the
Solar System that we know of appeared.
This is the model of the Pythagorean
Philolaus (c.470--c.385 BCE).
See Philolaus (c.470--c.385 BCE)
and Pythagoras (c.570--c.495 BCE)
in the figure below
(local link /
general link: pythagoras.html).
The Philolaic system
is illustrated in the figure below
(local link /
general link: philolaus_cosmos.html).
Philolaic system
was remembered in later
Classical Antiquity
and later ages, but was NOT influential.
After the
Copernican heliocentric solar system
was introduced in 1543, some
people referred to it as the
Pythagorean system
(meaning the Philolaic system)???
because they vaguely thought of
the Copernican system
as revival of the Pythagorean
Philolaic system---which
was absolutely NOT the case.
From about 4th century BCE, most
astronomers in Classical Antiquity,
the Islamic Golden Age (c.9th--13th centuries),
and
Medieval Europe
thought in terms of a finite universe enclosed by a
celestial sphere of the stars
thought of as a real surface with surrounding an unmoving spherical
Earth at the center.
They were thinking of a purely GEOCENTRIC, FINITE COSMOS (with the
Earth at rest).
They were following Aristotle (384--322 BCE)
in this regard---we get to him in the section Aristotle.
The ancient Greek astronomers
did try to qualitatively and quantitatively understand the GEOCENTRIC, FINITE COSMOS.
This work began with
Eudoxus of Cnidus (410 or 408--355 or 347 BCE).
The figure below
shows a simplified version of the
Eudoxon model
for explaining the motion of the
Sun around the Earth
and expands on
Eudoxon models in general.
Caption: The
Eudoxon model
for explaining the motion of the
Sun around the Earth.
The Eudoxon models
of planetary motion were invented by
Eudoxus of Cnidus (410 or 408--355 or 347 BCE).
At the quantitative level, Eudoxon models
did NOT succeed in explaining planetary motion.
Even qualitatively, their success is limited.
But you have to begin somewhere.
They are GEOCENTRIC, FINITE COSMOS MODDELS.
We do NOT know to what extent
Eudoxus considered
the Eudoxon models
to be physically real.
In the
Eudoxon models,
the fixed stars
are pasted on
celestial sphere of the stars
thought of as a real surface with surrounding an unmoving spherical
Earth at the center.
The celestial sphere of the stars
rotates around the Earth once per day.
There are compounded
celestial spheres
to account for the motions of the
planets:
(which include the
Sun and
Moon in this context).
The figure illustrates the Sun sphere which carries the
Sun.
It rotates once per year relative to the
celestial sphere of the stars.
The compounded motion of
Sun sphere and celestial sphere of the stars
qualitatively
accounts for the motion of the Sun
on the sky.
This is also true in Aristotelian cosmology
which incorporates
Eudoxon models.
The Eudoxon models
were the first ones
to qualitatively explain the
more difficult celestial motions in terms of 3-dimensional geometric structures.
The more complex Eudoxon models
do qualitatively give
apparent retrograde motions
for the planets.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Recall that the word "apparent" in
astronomy does NOT mean "seeming", it means from
the perspective of the Earth.
The expression apparent retrograde motion
applied to Solar System bodies---which
is usually what one means if no other qualification is made---is motion
westward as seen from the
Earth which is opposite the
usual eastward motion of
Solar System bodies
seen from the Earth.
In modern usage retrograde motion
without the aqualifier "apparent"
means spatial motion opposite the usual spatial motion for the context.
In the context of the Solar System
the usual spatial motion is
counterclockwise
as viewed from the
north celestial pole (NCP).
To complicate matters at bit more,
apparent retrograde motion
is referred to just as retrograde motion
whenever that is what you mean which is often the case especially when
in context of pre-Copernican astronomy.
The meaning of words often depends on context.
php require("/home/jeffery/public_html/astro/ancient_astronomy/intellectual.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/hesiod.html");?>
To expand a bit on
Hesiod's
Theogony
and mythical cosmology in general,
see the figure below
(local link /
general link: leonardo_da_vinci_deluge_creation.html).
php require("/home/jeffery/public_html/astro/art/art_l/leonardo_da_vinci_deluge_creation.html");?>
The geneology of the
Greek gods---with
a few nifty additons by yours truly is shown in the figure below
(local link /
general link: theogony.html).
php require("/home/jeffery/public_html/astro/ancient_astronomy/theogony.html");?>
The overall structure of the universe in Theogony
is NOT well specified, but it may be a lot like the
Norse mythology universe:
dome of the sky,
underworld,
and
Midgard
(flat Earth and
ocean)
sandwiched between.
See figure below
(local link /
general link: cosmos_norse_yggdrasil.html)
showing a 19th century reconstruction
of the Norse mythology universe.
php require("/home/jeffery/public_html/astro/ancient_astronomy/cosmos_norse_yggdrasil.html");?>
Probably, many
mythological cosmologies were similar
to Greek
mythical cosmology
and the Norse mythology universe.
php require("/home/jeffery/public_html/astro/hellas/acropolis.html");?>
Philosophy
was born (by usual reckoning) in
Ancient Greece
circa the early
6th century BCE.
It's a glum fact that this colonization involved conquest and enslavement, but
in ancient times this was generally regarded as OK if you did it to others, but
NOT if it was done to you.
However, confidence also came from self-aware progressive
achievement in trade,
crafts,
art,
literature
(Homer (circa 700 BCE)
Hesiod (circa late 8th century BCE), etc.)
and sports
(e.g., ancient Olympic Games)---the
ancient Greeks generally thought
well of themselves---but who doesn't?
For Greek sculpture illustrated,
see the figure below
(local link /
general link: charioteer_delphi.html).
php require("/home/jeffery/public_html/astro/art/charioteer_delphi.html");?>
Societal confidence plus the fact that the
Archaic Greeks
were aware they had much to learn from older
societies of the ancient Near East
and ancient Egypt
made them relatively open to new ideas and innovations.
The Archaic Greeks
were, in fact, emerging from the
Greek Dark Ages (circa 1100--circa 800 BCE)
when they were illiterate and rather out of touch
with the world at large.
and have the mortals' own clothes and voice and form.
like mortals neither in form nor in thought.
but rather, seeking in the course of time, they discover what is better.
One special kind of debate that the
ancient Greek philosophers
carried on is called elenchos
and the logos is the
logic behind the argument.
As the John's Gospel puts it:
ην αρχη ην ο λογοσ
--- In the beginning was the logos.
See video
John 1 GREEK New Testament.
Free debate
the Archaic Greeks
had to some degree.
Actually in agrarian societies
like Classical Antiquity
(AKA Greco-Roman Antiquity),
90 % or more of the population
were illiterate
peasants
and had limited participation in the
high culture of their society
(see Wikipedia:
Roman Empire: GDP and income distribution).
Yours truly imagines the lives of the
peasants were like in
the novels by
Thomas Hardy (1840--1928) or
in The Potato Eaters:
see the figure below
(local link /
general link: vincent_van_gogh_potato_eaters.html).
php require("/home/jeffery/public_html/astro/art/vincent_van_gogh_potato_eaters.html");?>
That
ancient Greece
(prior to Alexander the Great (356--323 BCE)
and his father
Philip II of Macedon (382--336 BCE))
had pluralism
(multiple independent
city-states)
and at the same time unity
(same language,
culture, mythology)
was probably of critical importance in the
development of impressive natural philosophy.
There could be many experiments in thought and at the same wide cultural communication.
php require("/home/jeffery/public_html/astro/art/art_m/melancholia.html");?>
Of course, some
natural philosophers
did do
experimentation and/or
detailed observations.
But the
scientific method
was NOT explicit in reports of their work.
php require("/home/jeffery/public_html/astro/ancient_astronomy/presocratic_timeline.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/socrates_death.html");?>
php require("/home/jeffery/public_html/astro/maps/map_ionia.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/ionia_samos.html");?>
The most prominent Presocratics are
Thales (c.624--c.546 BCE),
Anaximander (c.610--c.546 BCE),
Anaximenes (c.585--c.528 BCE),
and Pythagoras (c.570--c.495 BCE)
all in the 6th century BCE.
php require("/home/jeffery/public_html/astro/art/art_h/hecate.html");?>
Thales---the first
philosopher by everyone's
reckoning---thought the basic substance was water,
Anaximander
thought it was the apeiron (i.e., the Boundless),
and
Anaximenes thought it was
air.
php require("/home/jeffery/public_html/astro/ancient_astronomy/pythagorean_sunrise.html");?>
Another core belief of
Pythagoreans was in
metempsychosis
(their version of reincarnation).
By the by, most of what yours truly knows about the
Presocratics
comes from
David Furley (1922--2010),
The Greek Cosmologists, 1987.
David Furley (1922--2010)
was the last Presocratic.
php require("/home/jeffery/public_html/astro/ancient_astronomy/democritus.html");?>
php require("/home/jeffery/public_html/astro/newton/newton_atoms.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/cosmology_atomist.html");?>
The use of vortices
in the
atomist cosmology
was a remarkable insight/lucky guess
since
vortices are
important ingredients in
star formation and
galaxy formation.
php require("/home/jeffery/public_html/astro/art/art_l/leonardo_da_vinci_deluge.html");?>
The idea of the
celestial sphere as the inner surface
of membrane swirled by a
vortex
is easy to appreciate when you think about how the
celestial sphere
rotates around the Earth.
php require("/home/jeffery/public_html/astro/celestial_sphere/sky_swirl_polaris_animation.html");?>
php require("/home/jeffery/public_html/astro/hellas/hellenic_theatre_segesta.html");?>
Parmenides
is probably the first person in
recorded history to propose the
spherical Earth theory
(see, e.g.,
Fu-41,56).
The figure below
(local link /
general link: parmenides_earth.html)
discusses his proposal and his reasons for it.
php require("/home/jeffery/public_html/astro/ancient_astronomy/parmenides_earth.html");?>
Besides philosophical reasons,
Parmenides
may have had 3 empirical reasons for proposing
a spherical Earth
that were known to later writers.
These empirical reasons for the
spherical Earth theory were:
Assuming the spherical Earth theory
and that the Sun is
very distant from the Earth,
it is possible using measurements of shadow lengths at
different latitutes and a bit of geometry to find the
circumference and radius of the
Earth.
This was done by
Eratosthenes (c.276--c.195 BCE).
See the figure below
(local link /
general link: eratosthenes.html).
Question: As you go farther north,
stars close to the
north celestial pole (NCP) are:
Answer 1 is right.
php require("/home/jeffery/public_html/astro/celestial_sphere/horizon_types_formula.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/eratosthenes.html");?>
The spherical Earth theory
was a tremendous advance in
Greek astronomy
and in human knowledge.
php require("/home/jeffery/public_html/astro/ancient_astronomy/distance_problem.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/philolaus_pythagoras.html");?>
We call
the model of Philolaus
the Philolaic system.
php require("/home/jeffery/public_html/astro/ancient_astronomy/philolaus_cosmos.html");?>
A key feature of the
Eudoxon models
is that the
planets
(including the Sun
and Moon)
are never change their distances from the
Earth.
Similar, but more complicated,
Eudoxon models
(with rotation rates fitted to the observations)
account qualitatively
for the motions of the other planets.
Question: Apparent retrograde motion
is when a planet moving on the
celestial sphere
relative to the fixed stars moves:
Answer 2 is right.
Aristotle (384--322 BCE)
is, of course, a famous Greek philosopher---in fact,
the Greek philosopher
par excellence to many---and
for long ages, the Philosopher.
Why?
Aristotelianism
(i.e., Aristotelian philosophy) seemed for
two millennia up to circa 1600
in western Eurasia
to offer a complete system---to
those who had ever heard of it---though of course, NOT
all of these accepted everything or anything.
It seemed to many to be all reason could tell you.
It had a long vogue.
In his actual lifetime among other things,
Aristotle
established a school, the Lyceum in
Athens, in order
propagate the
liberal arts
(as we would call them),
natural philosophy,
and philosophy in general.
But NOT in the Parthenon
on the Acropolis of Athens.
See figure below
(local link /
general link: acropolis.html).
Aristotle also contributed
to Greek astronomy by
theorizing
Aristotelian cosmology
which we summarize in the figure below
(local link /
general link: aristotle_cosmology_summarized.html).
We expand on the summary in the subsections below.
As discussed in the above
subsection The Spherical Earth Theory,
the ancient Greeks
had valid reasons for believing the
spherical Earth theory
by Aristotle's (384--322 BCE) time.
Aristotle summarized most of the
valid reasons for believing it
as mentioned in the subsection The Spherical Earth Theory.
It seemed obvious that the Earth
was at rest and the Heavens
revolved around it.
Clearly the Earth was a special place
and could reasonably identified as the center.
Aristotelian cosmology
like most ancient cosmologies is geocentric.
In a sense, it would make the
universe more rational if
the Earth rotated daily on an
Earth axis.
Then the universe would NOT
have to race around the
Earth at colossal velocities.
Aristotle's contemporaries
Hicetas c.400--c.335 BCE
and Heraclides Ponticus (c.390--c.310 BCE),
in fact,
suggested that the Earth rotated daily
on its axis as an explanation
of the diurnal rotation
of the celestial sphere.
This suggestion was NOT accepted by almost everyone.
Aristotle
(and other ancient Greeks)
argued that the Earth had to be at rest
since otherwise we would be spun off or blown off by terrific winds.
In any case, we would feel the motion. See the figure below for feeling it.
The location on the Earth's surface
defines a local inertial frame
to high accuracy/precision
for most purposes.
Recall that relative to
inertial frames,
Newton's laws of motion
apply directly: e.g., in a smoothly moving unaccelerated train or plane.
There are no
inertial forces
(AKA fictitious forces)
unless you accelerate: speed up, slow down, or turn.
Now the Earth's
surface is slightly accelerating since
the Earth rotates on its axis
and has other smaller accelerations
in space
too, but these accelerations
are below human perception, and thus
so are the accompanying inertial forces.
Also the motion of the surface and everything on it is smooth. There are no jolts except for the
occasional earthquake.
So we on the surface of the
Earth sense NO
acceleration
and almost everyone up to circa 1600
thought that that meant NO motion.
In defense of a non-moving
Earth,
Aristotle did note that there was
NO observable
stellar parallax---see
the figure below for an explication of
Aristotle's argument and why it turned out to be wrong.
Aristotle's main new
development in cosmology was just
to specify a complete set of
Eudoxon models
for all the known
Solar System bodies.
Aristotelian cosmology is explicated
in the figure below
(local link /
general link: aristotle_cosmos.html).
Uniform circular motion
in Aristotelian cosmology
and in ancient Greek astronomy in general
is explicated in the figure below
(local link /
general link: uniform_circular_motion_ancient.html).
According to Aristotle,
beyond the celestial sphere of the stars
was nothing---NOT even empty space---just nothing
(e.g., Fu-137).
The Aristotelian universe was a finite
bounded sphere.
But it was also eternal---unbounded in time.
Aristotle had arguments for these conclusions---but
we won't go into them---they were WRONG.
The figure just below
(local link /
general link: aristotle_hoplite_spear.html)
expands a bit on bounded
the Aristotelian cosmos.
The Earth, on the other hand, was imperfect and changing.
Well the spherical Earth model
is correct and Aristotelian cosmology
does explain, incorrectly, but adequately relative to the
Ancients
why they did NOT observe stellar parallax.
Otherwise, it is mostly wrong.
But even as wrong, it could still give a correct description of the
motions of the Solar System bodies.
Qualitatively, it does although NOT very well I think???.
Quantitatively, it is NOT a good description.
You CANNOT produce accurate ephemerides from
Aristotelian cosmology.
I don't know that anyone ever tried to.
Strict Aristotelians---those pesky
varmits---rationalized that
Aristotle
had got it right as far as human understanding could reach.
For Aristotle (384--322 BCE),
the "supreme authority"
see the figure below
local link /
general link: aristotle_supreme.html).
Thus, in principle, Aristotelian cosmology
is a useful hypothesis in that it provides the basis for refinement and counter-theories.
It did, in fact, fulfill this role, but NOT very well.
Nevertheless,
for nearly 2000 years in western Eurasia,
Aristotelian cosmology
became a philosophical dogma to many intellectuals.
For those people, it was just be accepted with only minor corrections.
Why was this so?
In later Classical Antiquity,
Medieval Islamic society,
Medieval Europe,
and Renaissance Europe,
Aristotle
for many intellectuals---but NOT all---became
the highest or even the SUPREME AUTHORITY in
philosophy including
natural philosophy.
Aristotle seemed to offer to the
intellectual or educated person a complete
philosophy---except
in the religious dimension.
And, of course, there is a reason for this---he was a broad and deep thinker.
And he did offer the aforementioned reasoning for
Aristotelian cosmology.
To us, NOT very compelling reasoning, but for
nearly 2000 years in western Eurasia
some people thought it was good enough.
Also, it has to be said that the preeminence
of
Aristotle was partially just an accident of
history.
Once Aristotle was taken
as the highest or even the SUPREME AUTHORITY, the conservativism of
traditional societies tended to keep him being
top dog.
By being dogmas, they became impediments to advances in
nature knowledge rather
than theories that advance research.
Form groups of 2 or 3---NOT more---and tackle
Homework 4
problems 11--17 on the ancient Greek astronomy.
There's a hint for problem 14.
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/aristotle/aristotle.html");?>
php require("/home/jeffery/public_html/astro/hellas/acropolis.html");?>
php require("/home/jeffery/public_html/astro/aristotle/aristotle_cosmology_summarized.html");?>
The planets,
Sun,
and Moon
all seemed to revolve around the
Earth directly.
The fixed stars
revolved around the celestial axis
which passed through the
spherical Earth which
was known to be small compared to the
Heavens.
Also things fell down to the Earth,
whereas in the Heavens
things moved in circles it seemed.
php require("/home/jeffery/public_html/astro/art/art_o/ox_cart.html");?>
In modern physics,
we understand why we do NOT notice the tremendous
angular velocity of the
Earth.
php require("/home/jeffery/public_html/astro/aristotle/aristotle_stellar_parallax.html");?>
php require("/home/jeffery/public_html/astro/aristotle/aristotle_cosmos.html");?>
The whole Aristotelian cosmological system
in simplified form
with most of the celestial spheres omitted
is shown in a simplified illustration from
Renaissance Europe
shown in the figure below
(local link /
general link: aristotle_cosmos_system_renaissance.html).
php require("/home/jeffery/public_html/astro/mechanics/uniform_circular_motion_ancient.html");?>
php require("/home/jeffery/public_html/astro/aristotle/aristotle_hoplite_spear.html");?>
Question: Aristotle probably mainly thought
the Heavens were
were perfect and unchanging because:
Certainly 2, but maybe 1 also.
Aristotle
did think of the Heavens
as being the divine realm and the
prime movers (AKA unmoved movers)
of the Heavens
as being gods in a sense.
But Aristotle does
NOT seem to view these gods
as objects of worship
(e.g., Co-20--21, 148).
They were as conscious beings---ones who think only thinking itself
(see Wikipedia:
Unmoved mover: Aristotle's theology).
php require("/home/jeffery/public_html/astro/aristotle/aristotle_supreme.html");?>
On the other hand, Aristotelian cosmology
provided a complete
cosmology supported by
some observations and some reasoning.
Traditional societies are often very conservative.
Conventions, habits, beliefs, procedures just do NOT get questioned or
changed very often.
Particularly relevant to the
history of astronomy is that
Aristotelian physics and,
as mentioned above,
Aristotelian cosmology
became philosophical dogmas.
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_3.html");?>
Group Activity:
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
But to recapitulate, his Eudoxon models of compounded celestial spheres of the astronomical objects were the essence of Aristotelian cosmology and very qualitatively they could account for planetary motions including apparent retrograde motions.
As a mathematician, he was the greatest expert on ellipses until circa 1500 CE, but he did NOT use them for planetary orbits---if he did work planetary orbits which is NOT certain.
We explicate in the figure below (local link / general link: ellipse_animation.html).
Hipparchus' greatest discovery
was the discovery of the
axial precession (AKA
precession of the equinoxes)
(see Wikipedia:
Hipparchus: Precession of the equinoxes).
See the imaginative portrait
of Hipparchus in the figure below
(local link /
general link: hipparchus.html).
php require("/home/jeffery/public_html/astro/mathematics/ellipse_animation.html");?>
php require("/home/jeffery/public_html/astro/ancient_astronomy/hipparchus.html");?>
With the epicycle models,
Ptolemy
could quantitatively predict the motions of the
planets
(including the Sun and Moon)
and, in particular, explain their
apparent retrograde motion
which he, like all the almost all the Ancients,
regarded as spatial
retrograde motions.
Although NOT a strict
Aristotelian,
Ptolemy basically followed
Aristotelian physics
and, in some respects,
Aristotelian cosmology.
Ptolemy does NOT say who "They" are.
But he is probably thinking of
Hicetas (c.400--c.335 BCE)
and
Heraclides Ponticus (c.390--c.310 BCE)
who we mentioned above in subsection
Why Earth at Rest?
as suggesting a rotating Earth
and
Aristarchos of Samos (c.310 -- c.230 BCE)
and Seleucus of Seleucia (fl. 150 BCE)
who we will discuss below in section Aristarchos.
A model like this could be constructed for all the planets
(including the Sun and Moon).
Some extra complicating features were needed by
Ptolemy
to get good fits to the observations.
Ptolemy
presented his complete
epicycle model
for the geocentric solar system model
in his book the Almagest as we call it.
The Almagest
is a triumph of ancient
mathematical astronomy
and the greatest and last monument of
ancient Greek astronomy.
We call this complete
epicycle model
the Ptolemaic system.
The full
Ptolemaic system
is illustrated in a cartoon in the figure below
(local link /
general link: ptolemy_system.html).
The Ptolemaic system
has deficiencies:
Obviously, the
Ptolemaic system
it is wrong as we know today.
So it could only be a step in the
cycle of the scientific method.
This deficiency is one that can only be recognized as a fact after
more cycling through the
scientific method.
However, the fact, that predictions of
Ptolemaic system
were NOT perfect suggested in times after
Ptolemy
that the Ptolemaic system
was NOT perfect.
Although until Nicolaus Copernicus (1473--1543),
a radical change away from the
Ptolemaic system
as a calculating tool was NOT suggested.
The Ptolemaic system
is NOT
consistent with Aristotelian cosmology---which
has NO epicycles.
In fact, the epicycle motions
CANNOT be reproduced by compounded
celestial spheres
of Aristotelian cosmology.
A key point is that
epicycles
require Earth-planet
distances to vary and this is NOT allowed by
compounded
celestial spheres.
Ptolemy in another book,
Planetary Hypotheses
(see the figure below
(local link /
general link: ptolemaic_physical_model.html)
attempted a compromise with
Aristotelian cosmology.
But this compromise was NEVER accepted by
strict Aristotelians.
In their view,
the Ptolemaic system
was just a calculating device that
saved the phenomena (and they were right)
and Aristotelian cosmology
was right insofar as human reason could go (and they were wrong).
The lack of consistency between
the Ptolemaic system
and Aristotelian cosmology
seems unimportant to us since both theories are wrong.
But this presentism.
To the proponents of the two theories, it was a vital issue.
It is possible that many
astronomers and
philosophers through later
Classical Antiquity
and the Middle Ages
in the Mideast
and Europe
had no definite opinion on the respective
validity of
the Ptolemaic system
and Aristotelian cosmology.
They may have sat on the fence.
Strict Aristotelians
didn't sit on the fence.
See the figure below
(local link /
general link: avicenna.html)
of a Medieval
Aristotelian.
The structure of the Solar System is NOT determined: i.e.,
the order and relative distances to the
Solar System
are NOT integral parts of the
Ptolemaic system.
It is NOT a coherent model of the
Solar System.
You could use the
Ptolemaic system
for astronomical predictions and calculating
ephemerides
without specifying order and relative distances.
This is true for any
geocentric
epicycle model
unless one makes extra hypotheses.
In the Almagest,
Ptolemy
adopted standard ancient Greek astronomy
ordering
(going outward Moon,
Mercury,
Venus,
Sun,
Mars,
Jupiter,
Saturn,
celestial sphere of the stars)
based probably on the argument we gave in the figure above
(local link /
general link: ptolemy_system.html).
Ptolemy did, in fact, make extra hypotheses
in order to determine the distances to the
astro-bodies
in his book
Planetary Hypotheses:
see the explication in the figure below
(local link /
general link: ptolemaic_physical_model.html).
It is a credit to
Ptolemy's
scientific ambition that he
did write
Planetary Hypotheses,
but it does NOT seem to have led to any further research in and of itself
in later astronomy history
and, of course, the hypotheses in it are WRONG.
Ptolemy
actually needed more tricks than in the
ideal epicycle model
in order to fit the observations well: i.e.,
to save the phenomena.
One of these
tricks was that he made Earth off-center making the
circular orbits eccentric.
So his models weren't exactly geocentric.
This was a violation of a key axiom of
Aristotelian physics and
Aristotelian cosmology
Strict Aristotelians objected to this.
And Ptolemy
would have to admit an inconsistency in his own thinking since
he was fairly
Aristotelian himself---NOT
that he ever did admit it in the
historical record.
Another trick was the equant.
Ptolemy most
scandalous trick was
the equant---it was
the crime of Ptolemy.
For equant and the crime,
see the figure below
(local link /
general link: ptolemy_epicycle_equant.html).
Plato (428/427--348/347 BCE)
and Aristotle
had proclaimed that uniform circular motions
were all that could be allowed for elementary astronomical motions.
Complicated motions were constructed by compounding
uniform circular motions
with
Aristotle's
celestial spheres or
by epicycle models.
Ptolemy
agreed in principle, with the
dogma of uniform circular motion,
but violated the dogma by making
deferent
angular velocities constant around an
equant
which was displaced from the center of the
deferent
on the opposite side from the Earth's
displaced-from-the-center position.
To modern science,
the introduction of the equant
is an unimportant issue, but to later
astronomers working with the
Ptolemaic system,
it was a serious defect that implied that
the Ptolemaic system
was NOT completely realistic since
it violated a philosophical/physical dogma that was assumed to be
Plato-given truth.
Since Ptolemy's models
are imperfect and the observations setting their
parameters
(i.e., controlling variables)
are imperfect,
the predictions of the models will deviate from observations and those deviations
will increase with time.
As the centuries rolled by
after Ptolemy, the
parameters had
to be updated, but the updates were often pretty imperfect too.
Of course, modern models of Solar System
motions suffer the same problem.
However, the size of the deviations for modern models is much, much smaller.
Finally and most importantly,
the
Ptolemaic system
was NOT a unique
fit to the observations with
epicycle models.
By varying the size of the
deferent
and epicycles
and adding epicycles on
epicycles,
varying the orbital speeds,
and fooling around with the equant,
you can create endless models
that give the same predictions to within about the same accuracy as those
of the Ptolemaic system.
There was no way to tell which
epicycle model was right.
In fact, none of them are as we know now.
If the Ancients
had been able to measure
Solar System distances
beyond the Moon,
they would have known this.
But they couldn't have measured such distances.
Ptolemy was such a clever
model builder that he must have at least suspected the
non-uniqueness problem, but he doesn't discuss it.
He probably hoped that a sufficiently accurate
epicycle model would
approach the unique true cosmological model
and that his Ptolemaic system
did approach the unique true cosmological model.
Or perhaps, he indulged in wishful thinking about how good
the Ptolemaic system was.
For 13 centuries
after Ptolemy,
astronomers working in the
traditions of
Indian astronomy,
Medieval Islamic astronomy,
Medieval European astronomy,
and
Renaissance astronomy
would try to develop epicycle models
that improved on the
Ptolemaic system.
They found epicycle models
that were as accurate, but NOT really more accurate and they couldn't tell which was right.
Of course, unlike 7,
the Solar System really does have unique structure.
After Ptolemy (c.100--c.170 CE)
in the 2nd century CE,
the great age of Greek astronomy was over.
There were NO more great advances.
But there were a few
Keepers of the Flame---i.e.,
the tradition/techniques of
Greek astronomy.
Theon of Alexandria (c.335--c.405 CE),
possibly in collaboration with his daughter
Hypatia (c.360--415 CE)
(see the imaginative portrait
in the figure below:
local link /
general link: hypatia.html),
wrote commentaries and/or edited the works
of Ptolemy.
But after that there is NOT much more to say.
But we can go backward a bit to discuss
Aristarchos of Samos (c.310--c.230 BCE)
in section Aristarchos.
php require("/home/jeffery/public_html/astro/ptolemy/ptolemy_armillary.html");?>
The
Ptolemaic system
and Aristotelian cosmology
have many things in common---they are both
geocentric,
both posit in uniform circular motion
as the fundamental elementary motion
out of which all other Solar System
are constructed by compounding
uniform circular motions.
Actually,
the Ptolemaic system
violates the dogma of
uniform circular motion
with the
abominable equant: see below.
Both
Ptolemaic system
and Aristotelian cosmology
a real celestial sphere of the stars.
Ptolemy did admit non-geocentric models
were geometrically possible,
but he thought that they were physically absurd:
... but think that there could be no evidence to oppose their view ...
or if they made both
heaven
and Earth move by
any amount whatever,
provided, as we said, it is about the same axis and in
such a way as to preserve the overtaking of one by the other.
However, they do NOT realise that, although there is perhaps nothing in the
celestial phenomena which would count against that hypothesis, at least from
simpler considerations, nevertheless from what would occur here on
Earth and in the
air, one can
see that such a notion is quite ridiculous.
A simple epicycle model is shown and
explicated in the figure below
(local link /
general link: epicycle.html).
---Ptolemy (c.100--c.170 CE)
in the Almagest,
Gerald J. Toomer's (1934--)
translation
Ptolemy's Almagest, (1998),
p. 44--45.
php require("/home/jeffery/public_html/astro/ptolemy/epicycle.html");?>
The animation
in the figure below
(local link /
general link: helio_geo_epicycle_animation.html
illustrates how
apparent retrograde motion
(i.e., westward motion
of the planet on the sky)
can be reproduced by an
epicycle model.
php require("/home/jeffery/public_html/astro/ptolemy/helio_geo_epicycle_animation.html");?>
php require("/home/jeffery/public_html/astro/ptolemy/ptolemy_system.html");?>
php require("/home/jeffery/public_html/astro/astronomer/avicenna.html");?>
php require("/home/jeffery/public_html/astro/ptolemy/ptolemaic_physical_model.html");?>
A uniform circular motion
means a constant tangential speed
(in, e.g., km/s)
moving around a
circle.
This was philosophical/physical dogma that conformed to the
supposed perfection of circles
and allowed one to avoid head-on confrontations with non-constant speeds.
php require("/home/jeffery/public_html/astro/ptolemy/ptolemy_epicycle_equant.html");?>
The plethora
of epicycle models
that were created
reminds me of the plethora of modern
inflation cosmology models.
Maybe inflation cosmology models
are the epicycle models of our time
and will one day go away.
Epicycle models
are, in fact, mathematical decompositions of the
Solar System motions---non-unique ones.
Question: What is 7 really?
Answer 3 is right.
Question: In order to break the deadlock of
epicycle models
and discover the true structure of the Solar System,
you had to have:
The rightest answer is 4.
The first answer leads immediately to the second and,
in fact as we will show below in subsection
Heliocentrism, having the second answer
leads immediately to the first.
php require("/home/jeffery/public_html/astro/ancient_astronomy/hypatia.html");?>
Yes. Aristarchos of Samos (c.310--c.230 BCE) about 4 centuries before Ptolemy (c.100--c.170 CE). See the figure below (local link / general link: aristarchos.html).
It's reasonable to guess, that Aristarchos was led to heliocentrism by the same reasons that led Copernicus.
We'll discuss those reasons below in the section Nicolaus Copernicus (1473--1543) and Heliocentrism.
Form groups of 2 or 3---NOT more---and tackle
Homework 4
problems 11--17 on the ancient Greek astronomy.
There's a hint for problem 14.
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/ancient_astronomy/aristarchos.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_3.html");?>
Group Activity:
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chartres_portail_royal_3.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chartres_portail_royal_2.html");?>
The Medieval astronomers
in the traditions of
Indian astronomy,
Medieval Islamic astronomy,
Medieval European astronomy,
and
Renaissance astronomy
continued to fiddle around with
geocentric
epicycle models.
But didn't improve them. Why not?
The fact is epicycle models, as discussed above in subsection The Deficiencies of the Ptolemaic System, were wrong and just mathematical decompositions of the celestial motions.
But because epicycle models did work as calculating devices, the Medieval astronomers working with them were endlessly tantalized by them and the hope of improving them. A hopeless hope.
So there was a stoppage in the cycle of the scientific method in cosmological theory (i.e., Solar System models).
Essentially, the Ptolemaic system ruled over Medieval astronomys throughout western Eurasia.
But if the Medieval astronomers were stuck in a theoretical dead end in Solar System models, they made progress in other areas as we discuss below in subsection Medieval Progress in Astronomy.
Additionally, the Medieval natural philosophers of the same time and places as the Medieval astronomers who were also Aristotelians were mostly stuck in Aristotelian cosmology---but they seem to have been happy about that.
To see where the Medieval astronomers and Medieval natural philosophers lived, see the map of western Eurasia circa 1190 in the figure below (local link / general link: map_western_eurasia_1190.html).
The
Medieval astronomers
did make some new observations---some of which were modest lasting contributions to
astronomy.
In Medieval Islamic society,
a tradition of building great observatories was started that alas died away.
Just the way things worked out, not the way they had to work out.
The observations from those observatories seem to have little lasting impact.
However, probably the progress in astronomical instrumentation made in the observatories
did having a lasting impact when communicated in some way to
Medieval astronomers
in Europe.
For an example of astronomical instrumentation, see
the Fakhri mural sextant
at the
Samarkand Observatory
in the figure below
(local link /
general link: samarkand_observatory.html).
The mathematical astronomers
did, however, improve MATHEMATICAL TECHNIQUES---a lasting contribution.
The trigonometric functions
were developed in
the
Medieval Indian society
and the Medieval Islamic society
(see Wikipedia: Trigonometry: History).
Of course, the ancient Greek astronomers
could do trigonometry, but
their methods were klutzy.
Also
Arabic numerals were introduced
(see Wikipedia:
History of the Hindu-Arabic numeral system)
and these eventually replaced the
clumsy numeral systems of the past:
e.g.,
cuneiform numerals,
Greek numerals, and
Roman numerals.
A duodecimal system (i.e., base-12 system)
might have been handier, but since our hands have 10 fingers . . .
Decimal fractions
also started to come into use.
They seem to have been developed independently several times
(see Wkipidia:
Decimal system: History of decimal fractions).
An important treatise on them was written
by Jamshid Al-Kashi (c.1380--1429)
who worked at
Samarkand Observatory
(see
John North 1994, The Norton History of Astronomy and Cosmology, p. 1200).
In Europe, just a bit later
and probably independently
Giovanni Bianchini (1410--c.1469)
used decimal fractions
and may have been the first to use the
decimal point
(see
Wikipedia: Giovanni Bianchini (1410--c.1469)).
However, his decimal point
work was not well known though it seems to have been passed on to some later
Renaissance astronomers
and
early modern astronomers.
Simon Stevin (1548/9--1620) later
greatly promoted the use of
decimal fractions
in the Europe
(see Wikipedia: Simon Stevin:
Decimal fractions).
Nicolaus Copernicus (1473--1543)
it seems he did NOT use
decimal fractions
(see
De revolvtionibvs orbium coelestium (1543, p. 110 facsimile of
On the Revolutions of the Heavenly Spheres (1543)).
There are many
Medieval astronomers,
but except to very interested persons,
their names are mostly unknown and their accomplishments tedious to tell of.
But there are three who
are moderately well known---for reasons
other than astronomy---the
Persian
Al Khwarizmi (c.780--c.850),
the also Persian
Omar Khayyam (1048--1123),
and the Englishperson
Geoffrey Chaucer (c.1343--1400)
(see also Writers: Geoffrey Chaucer (c.1343--1400)).
The
Medieval Islamic mathematician
Al Khwarizmi (c.780--c.850)
is explicated a bit in the figure below
(local link /
general link: al_khwarizmi.html).
For Omar Khayyam (1048--1123),
see the two figures below
(local link /
general link: omar_awakening.html;
local link /
general link: omar_reading.html).
Geoffrey Chaucer (c.1343--1400)
can only be considered an amateur adept
in astronomy, but he did write
A Treatise on the Astrolabe (1391).
For more on Chaucer,
see the two figures below
(local link /
general link: chaucer_astrolabe.html;
local link /
general link: chaucer_astrolabe_like.html).
php require("/home/jeffery/public_html/astro/maps/map_western_eurasia_1190.html");?>
Just try doing division
in Roman numerals---what fun.
With Arabic numerals beginning
to dominate in western Eurasia,
the decimal system (i.e. base-10 system)
also began to dominate there.
php require("/home/jeffery/public_html/astro/astronomer/samarkand_observatory.html");?>
php require("/home/jeffery/public_html/astro/astronomer/al_khwarizmi.html");?>
php require("/home/jeffery/public_html/astro/omar_khayyam/omar_awakening.html");?>
php require("/home/jeffery/public_html/astro/omar_khayyam/omar_reading_2b.html");?>
php require("/home/jeffery/public_html/astro/writer/chaucer/chaucer_astrolabe.html");?>
php require("/home/jeffery/public_html/astro/writer/chaucer/chaucer_astrolabe_like.html");?>
But Chaucer
certainly was a poet.
See the figure below
(local link /
general link: chaucer_17th_century.html).
php require("/home/jeffery/public_html/astro/writer/chaucer/chaucer_17th_century.html");?>
The figure above
(local link /
general link: chaucer_17th_century.html)
alludes to the Chauntecleer story
which is
The Nun's Priest's Tale
from The Canterbury Tales (1387--1400).
For The Canterbury Tales,
see the figure below
(local link /
general link: chaucer_canterbury_tales_mural.html).
php require("/home/jeffery/public_html/astro/writer/chaucer/chaucer_canterbury_tales_mural.html");?>
The company of pilgrims
of The Canterbury Tales (1387--1400)
assembles at The Tabard Inn.
See the figure below
(local link /
general link: chaucer_tabard_inn.html).
php require("/home/jeffery/public_html/astro/writer/chaucer/chaucer_tabard_inn.html");?>
The arrival at Canterbury
(see the figure below:
local link /
general link: canterbury.html)
was the intended end of
The Canterbury Tales---the
end of pilgrimage.
php require("/home/jeffery/public_html/astro/art/art_c/canterbury.html");?>
php require("/home/jeffery/public_html/astro/copernicus/copernicus_portrait_3.html");?>
Strict Aristotelians probably believed Aristotelian cosmology was the best human understanding could do.
Ptolemy, himself, certainly must have hoped that his extension of Ptolemaic system in the semi-Aristotelian Ptolemaic physical model was physically realistic.
But Ptolemy was such a clever builder of epicycle models that he should have known that neither the Ptolemaic system nor the Ptolemaic physical model was a uniquely good fit to the observations even if their basic assumptions were correct in his view.
The general opinion among the natural philosophers of the 15th and 16th centuries in European context may have been Aristotelian cosmology was essentially right, but that reality was too complex to make it mathematically predictive.
Of course, there are no opinion polls from the past, and so we must glean our knowledge of what the natural philosophers were thinking largely from what typical ones said.
Medieval professors and their immediate successors Renaissance professors mostly. For a Medieval professor in action, see the figure below (local link / general link: medieval_professor.html).
There were some other kinds of persons who were natural philosophers or at least persons interested in cosmology, but they were probably mostly university-educated persons.
"What is truth?" as Copernicus may have asked.
Nicolaus Copernicus (1473--1543) was German-Polish, physician, economist, and Church official and lawyer (of the Catholic Church). For more on Copernicus, see the figure below (local link / general link: copernicus/copernicus_portrait.html).
php require("/home/jeffery/public_html/astro/copernicus/copernicus_portrait.html");?>
There has always been some question as to whether
Copernicus
considered himself
German or
Polish.
Probably both (see Wikipedia: Nicolaus Copernicus: Nationality).
He certainly spoke German and had a German cultural upbringing, but he probably spoke Polish too, and he was born in the Kingdom of Poland. Of course, he also knew and wrote in Latin as most scholars of his time did.
As a student in Italy, he enrolled as a German, but that may have just been to obtain certain privileges or conveniences open to being a German student (see Wikipedia: Nicolaus Copernicus: Languages).
Copernicus studied in Italy for most of the decade 1496--1506.
He was part of the time in Padua where he was at the University of Padua. Copernicus would have known---one assumes---the church of Sant'Antonio shown in the figure below.
Caption: Basilica of Saint Anthony of Padua (AKA Sant'Antonio) in Padua, Italy, under construction circa 1233--1301. Seen here in twilight.
Nicolaus Copernicus (1473--1543) in his student days (1501--1503) and Galileo (1564--1642) as professor of mathematics (1592--1610) would both have known Sant'Antonio.
They were both at University of Padua (founded 1222).
Copernicus studied astronomy, astrology, and medicine.
Galileo taught the first two subjects.
Astrology was considered a necessary qualification for medicine---just ask yourself would you trust a doctor who could NOT give you a diagnosis based on your stars.
Credit/Permission: ©
Ricardo Andre Frantz (AKA User:Tetraktys),
2005 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Padua9.jpg.
Maybe both. The small arches
look decorative, but the big ones
in the false doors look structurally necessary.
Using arches both for structural support and decoration was one of the best ideas of the Romans.
In the modern times, we often do NOT use arches in common buildings for structural support.
It's usually cheaper just to build a stronger lintel. We just stick in another steel I-beam girder. But when we really need maximum strength, we use arches too: often for, e.g., bridges and trestles.
Note our answer, mutatis mutandis, is also why planets and stars are ROUND. Their self-gravity overcomes pulls them into a round shape. Only compression resistance of their materials sustains them against collapse.
From the early years of the 16th century or maybe even earlier, Copernicus had become convinced that heliocentrism would solve the chief problem of astronomy: i.e., the fact that the structure of the cosmos was NOT really known.
Copernicus, by the way, was aware of Aristarchos of Samos (c.310 -- c.230 BCE) and the heliocentrism and partial heliocentrism in ancient Greek astronomy (see Wikipedia: Nicolaus Copernicus (1473--1543): Predecessors).
However, the ancient Greek astronomers left NO strong argument for heliocentrism---NO strong argument in the historical record that is.
Copernicus presented a detailed argument which is what eventually made heliocentrism non-ignorable.
Copernicus published his detailed theory in his book On the Revolutions of the Heavenly Spheres in 1543: the actual Latin title is De Revolutionibus Orbium Coelestium.
ONE DIAGRAM shown in the figure below (local link / general link: venus_elongation.html) shows you why Copernicus turned to heliocentrism---or at least why he should have.
php require("/home/jeffery/public_html/astro/copernicus/venus_elongation.html");?>
The procedure shown in the figure above
(local link /
general link: venus_elongation.html)
works just for
inferior planets.
The orbital radii of the
superior planets
can be found using a general procedure assuming the
heliocentric solar system model.
The general procedure is actually pretty easy, but it is a bit more than we want do here. See the General Procedure for Orbital Radius Determination for the general procedure and its derivation.
The general procedure was used by Copernicus (probably with a much klutzier formulation) to deduce all the planet orbital radii in the heliocentric solar system model.
Since heliocentrism gave the relative distances, the structure of the Solar System was revealed to Copernicus:
This quote suggests that Copernicus thought that the deduced structure of the Solar System was the main argument for heliocentrism.
Unfortunately, Copernicus never makes that completely explicit it seems. He certainly thought of it as a major argument. Retrospectively, it clearly is the main argument.
Copernicus' own not-to-scale diagram of the Copernican system (i.e., Copernicus' full model for the Solar System) is shown in the figure below (local link / general link: copernican_system.html).
php require("/home/jeffery/public_html/astro/copernicus/copernican_system.html");?>
Now the absolute distances were NOT known at all accurately since the
astronomical unit
was NOT known accurately
in terms of the Earth's size.
Only in the 17th century would the astronomical unit begin to be measured accurately (Wikipedia: Astronomical unit: History). Copernicus used the ancient Greek value for the astronomical unit which was about 23 times too small (see John North 1994, The Norton History of Astronomy and Cosmology, p. 294).
But Copernicus had found the "chief thing", NOT by new observations, but just by having the right theory.
Of course, heliocentrism could have turned out to be wrong.
But the modern way of judging theories which CANNOT be tested yet by observation is by how many important results can be deduced from them and how fruitful they are in leading to new developments.
In fact, even if a theory turns out to be wrong, it is still a GREAT THEORY if it is fruitful in furthering development---stimulating more research, suggesting better theories, be useful in teaching, just a darn brilliant idea, etc.
So even it had been wrong, heliocentrism was great theory because one can deduce from it important results that can be tested by observations that were in principle possible if NOT practicable yet in Copernicus' time.
Based on the deduced structure of the Solar System and other information and arguments, Copernicus became convinced that heliocentrism-predicted structure was right.
And we can agree---without going into all the details---that he was right to think it at least very probably right.
Copernicus' heliocentrism---or as one can call it in the century or so after Copernicus, Copernicanism---was recognized by as a great theory by those astronomers who we see retrospectively as most modern and progressive: the most important of these being Galileo Galilei (1564--1642) and Johannes Kepler (1571--1630) whom we cover below in, respectively, sections Johannes Kepler (1571--1630) and Galileo Galilei (1564--1642).
The Copernican system
(i.e., Copernicus' full model for
the Solar System)
in its details was in many ways entirely conventional
for Copernicus' time.
In order to make a predictive model for the construction
of ephemerides,
etc.,
Copernicus
had to use
epicycles,
uniform circular motion,
and other ancient devices.
He may believed that
epicycles
and
uniform circular motion,
had some sort of reality as fundamental elements of motion
just like the ancient Greek astronomers,
but it's hard to know.
He also still used the celestial spheres of
Aristotelian cosmology in some way.????
Why did Copernicus
want a predictive model anyway?
Among other things, he had to make the
Copernican system
a predictive model or
his contemporaries would NOT necessarily have
considered it seriously.
Probably, he himself believed it had to be predictive to have any chance
of being real.
In fact, except for the transposition of the
Earth
and Sun,
Copernicus'
epicycle models
are much like Ptolemy's in mathematical construction.
He was NOT an important innovator in the techniques of
mathematical astronomy.
Copernicus
did use relatively modern mathematical innovations such as
Arabic numerals
which made calculations a lot easier than using
Roman numerals.
However, it seems he did NOT use
decimal fractions
(see
De revolvtionibvs orbium coelestium (1543, p. 110 facsimile of
On the Revolutions of the Heavenly Spheres (1543)).
Copernicus
does NOT seem to have made any purely mathematical innovations himself.
In mathematical astronomy
per se,
a couple of noteworthy innovations
used by Copernicus are given below:
Modern scientists tend to see the equant and
the principle of
uniform circular motion
as dead isssues.
But this is presentism.
They were important issues to
astronomers from
Ptolemy (c.100--c.170 CE)
to Johannes Kepler (1571--1630).
Also it is still a living issue that scientific theories be self-consistent.
The equant and the principle of
uniform circular motion
were NOT consistent with each other.
So concern with their inconsistency is a mark of true scientific thinking.
See the animation
Ptolemy's (c.100--c.170 CE)
epicycle model
(with equant)
for Jupiter
in the figure below
(local link /
general link: ptolemy_epicycle_equant_animation.html).
One major improvement (by modern as well as ancient standards) of
Copernicus
over Ptolemy was a natural explanation of
apparent retrograde motion.
That explanation is given in the figure below
(local link /
general link: apparent_retrograde_motion.html).
But the epicycle
motion of astro-bodies
had always defied simple phyiscal explanation, except for it is just so.
Of course, Copernican system
uses epicycle models,
but in a heliocentric solar system.
So Copernicus still had
the physical inexplicableness of
epicycles,
but at least he had gotten rid of one reason for needing them.
Johannes Kepler (1571--1630)
would get rid of all epicycles
and all physical reasons for them.
Although Copernicus'
epicycle models
and mathematical techniques were NOT radical,
the implications for physics of
a true heliocentrism were completely radical.
The most obvious radical features are:
However, a key point of
Aristotelian physics
is that the Earth had to be at rest or else
we would feel its motion and everything would need obvious forces to keep moving with
the Earth.
But heliocentrism
demanded that the Earth
orbited the Sun
every year
AND rotated on its axis
every day.
Somehow every bit of the surface of the
Earth
had its own "frame of rest".
This is true to very good approximation, but
Copernicus could only
vaguely suggest this.
However, in fact,
Newtonian physics'
understanding of inertial frames
had to be corrected to the modern understanding
that all physical laws
are referenced to
inertial frames
(except for general relativity
which tells us what inertial frames
are to said modern understanding),
most elementary of which are
that are free-fall frames
NOT rotating relative to the
observable universe.
Non-inertial frames
can be turned into
inertial frames by the
use of inertial forces.
Every location on the surface of the
Earth is approximately
an elementary inertial frames
for most purposes and can be change into one exactly using
inertial frames.
For further explication of
inertial frames,
see Mechanics file:
frame_basics.html.
And although Copernicus used
epicycle models
and perhaps believed in them, sooner or later someone would find out they were wrong too.
That person would be
Johannes Kepler (1571--1630)
(see below section
Johannes Kepler (1571--1630)).
And if the
Earth was
a planet,
the other planets therefore could be like the
Earth---and therefore NOT be eternally unchanging
as posited by Aristotelian cosmology.
And they could have alien beings on them.
There were some early reactions to Copernicanism up to circa
1600.
In Europe, of course.
No else in the world would hear or think much of it for one or more
centuries.
Actually, the first 10 chapters of Book I of
On the
Revolutions of the Heavenly Spheres (1543) are qualitative and readable.
See Online text in
English translation: On the Revolutions of the Heavenly Spheres (1543)
(translation by Edward Rosen (1906--1985)).
Since their "betters" (i.e., the formal intellectual classes and
the aristocrats)
didn't believe or think much of
Copernicanism, the
"people" (everyone else) didn't bother much with it.
See the "people" in the figure below
(local link /
general link: vincent_van_gogh_potato_eaters.html).
But on the other hand,
they esteemed Copernicus' book as a
tour de force
of mathematical astronomy:
a proof that a modern could equal
Ptolemy (c.100--c.170 CE).
They were the ones who bought the 601
plus copies printed in the
16th century
(see
Wikipedia: De revolutionibus orbium coelestium Census of copies).
The post-Copernicus
Renaissance astronomers
also hoped that Copernican system
would be more accurate than the
Ptolemaic system
as a calculational device.
For example, the Prutenic Tables (1551)
of ephemerides
were based on the Copernican system
by mathematical astronomer
Erasmus Reinhold (1511--1553)
who did NOT accept it as physical reality.
Yours truly recalls reading somewhere that the
Prutenic Tables (1551) were actually
a bit more accurate than
those based on the
Ptolemaic system,
but only a modern computer study shows this???.
However, any improvement in accuracy was really pretty much accidental???.
It could only be a very minor heresy---it's only
about astronomy.
Note that Copernicus' life spanned the
early phases of
the Reformation (c.1517--c.1648)
and
Counter-Reformation (c.1517--c.1648)
and the beginning of
the wars of religion in Europe
and his hometown
Frombork (German Frauenberg) was on the frontier between
Catholic
and Protestant regions in
Poland.
See the map in the figure below
(local link /
general link: map_europe_1560.html).
So Copernicus was quite aware of the potential
heresy problem of
Copernicanism---he was
a Catholic Church lawyer after all.
In fact, one of the reasons for delaying publication of his theory until
he was near end of his life may have been to ensure he wouldn't
be around to face awkward questions.
We do NOT know this, but it's a reasonable hypothesis.
It sometimes said that the
heresy problem was NOT
a concern of Copernicus because
he never says anything about it.
But yours truly's opinion is that he did NOT mention it because
he really, really did NOT want to call anyone's attention to it.
As it turned out, the immediate religious reaction was muted.
On both Catholic
and Protestant sides, there was some negative feeling,
but a heresy in which no one believes doesn't excite a lot of official notice.
For some early Copernicans,
see the figure below
(local link /
general link: copernicans_early.html).
See the figure below
(local link /
general link: copernican_cosmos_digges.html)
of
Digges' illustration of
his suggestion for the universe.
php require("/home/jeffery/public_html/astro/ptolemy/ptolemy_epicycle_equant_animation.html");?>
php require("/home/jeffery/public_html/astro/copernicus/tusi_couple.html");?>
php require("/home/jeffery/public_html/astro/celestial_sphere/apparent_retrograde_motion.html");?>
In the Ptolemaic system
apparent retrograde motion
is modeled using
epicycles.
As mentioned in a figure above
(local link /
general link: ellipse_animation.html),
epicycles have had their
use in modern times as an analysis tool, but that use has
been criticized too and maybe they are on their way out of modern use
(Francis, C. 2011, arXiv:0911.1594v1,
"Lindblad's epicycles - valid method or bad science?").
The animation
in the figure below
(local link /
general link: helio_geo_epicycle_animation.html)
compares
apparent retrograde motion
as explained in
a heliocentric solar system model
and in a geocentric
epicycle model.
php require("/home/jeffery/public_html/astro/ptolemy/helio_geo_epicycle_animation.html");?>
The main point is that
Aristotelian physics and
Aristotelian cosmology
(with their unchanging Heavens and resting
Earth)
was totally wrong if Copernicus was right.
Copernicus and his contemporaries,
of course, had NO knowledge of the originial
understanding of
inertial frames
following from the original version of
Newtonian physics.
That would only come with
Isaac Newton's (1643--1727)
Principia (1687).
Newtonian physics
would demonstrate that
heliocentrism was correct in the sense
that it follows directly from
physical law.
php require("/home/jeffery/public_html/astro/art/vincent_van_gogh_potato_eaters.html");?>
php require("/home/jeffery/public_html/astro/copernicus/copernicus_heretic.html");?>
Thus, Copernicanism was potentially a
heresy on both sides of
the religious divide.
See the figure above
(local link /
general link: copernicus_heretic.html).
php require("/home/jeffery/public_html/astro/maps/map_europe_1560.html");?>
Copernicus
tried to defend his orthodoxy
of his theory by dedicating his book
to Pope Paul III (1468--1549, pope 1534--1549)
and addressing his book only to astronomers, NOT to
theologians or the general public.
php require("/home/jeffery/public_html/astro/copernicus/copernicans_early.html");?>
To explicate the
early Copernicans:
php require("/home/jeffery/public_html/astro/copernicus/copernican_cosmos_digges.html");?>
php require("/home/jeffery/public_html/astro/astronomer/giordano_bruno.html");?>
Form groups of 2 or 3---NOT more---and tackle Homework 4 problems 18--22 on Medieval Islamic astronomy, Medieval European astronomy, Renaissance astronomy, and Nicolaus Copernicus (1473--1543).
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
php require("/home/jeffery/public_html/astro/tycho/tycho_thor.html");?>
Tycho is one of those people who
history has decided to call by their first names---like
Galileo (1564--1642),
Napoleon (1769--1821),
and Ann-Margret (1941--).
Although Tycho rejected heliocentrism, his achievements greatly aided its advance from wild and crazy idea to the new paradigm of astronomy.
Tycho's rejection seems to have been strongly based on the idea that the Earth could NOT move. This giant massive body just could NOT rotate on its Earth's axis once per day NOR revolve around in Sun once per year at fantastic speeds. The celestial bodies were somehow ethereal and could move at fantastic speeds.
Note Tycho, like most of his contemporaries in astronomy, greatly esteemed Nicolaus Copernicus' (1473--1543) book De Revolutionibus Orbium Coelestium (1543) as a tour de force of mathematical astronomy while rejecting heliocentrism as physically absurd.
Tycho's great achievements in his renovation of astronomy can be discussed under 3 headings: 1) the aforementioned new observations of outstanding quality and quantity, 2) observations disproving key parts of Aristotelian cosmology, 3) the introduction of the Tychonic system.
We need to note that Tycho was the most famous astronomer of his day, and so his achievements were noted by other Renaissance astronomers and to some degree by the intellectuals in general and the general public.
We also need to note that his program of new observations was quite expensive requiring highly quality intruments and many assistants. He was supported financially by the King Frederick II of Denmark (1534--1588, reigned 1559--1588) (see Wikipedia: Tycho Brahe: Science and life on Uraniborg).
Tycho carried out a 20-year program of observational astronomy that achieved an accuracy never obtained before particularly for the planetary motions.
Actually, the Ottoman Turk polymath Taqi ad-Din (1526--1585) may have made astronomical observations of comparable accuracy to Tycho's just a bit earlier in history, but that data seems to have had little importance to the later development of astronomy.
His equipment (see the figure below) was NOT at all novel---in essentials, it had all existed for millennia. What was novel was his commitment to reducing observational errors.
Tycho perceived that one of the problems of astronomy as practiced up to his day was that new observations were often as poor as the old ones.
To RENOVATE ASTRONOMY you needed better observations, NOT just new ones. For Tycho at work on getting new better observations, see the figure below (local link / general link: tycho_wall_quadrant.html).
The importance of Tycho's data---particularly for planetary motions---comes with its use in the Solar System models of Kepler which we'll come to below in the section Johannes Kepler (1571--1630).
These were two:
In 1572,
Tycho observed a
new star
or, in Latin,
stella nova---a transient star-like
object that appeared and
then disappeared over the time of a few months.
We now recognize this
new star
as a supernova: a giant
explosion of an old star at the end of its lifetime---an example
supernova is shown in
the figure below
(local link /
general link: sn_1987a.html).
Tycho
did NOT discover this supernova.
It was extremely bright and could be seen by anyone on
Earth.
But he did make the most detailed observations of it.
But Tycho
did prove that the
new star
was beyond the Moon.
Thus he proved there was change in the
Heavens,
and thus that
Aristotle was wrong.
We now call this supernova
SN 1572 or
Tycho's supernova
or, for short, Tycho.
See Tycho's
sky map for
SN 1572 in the figure below
(local link /
general link: sn_1572_tycho_sky_map.html).
In 1577,
Tycho proved that the
Great Comet of 1577 was also
beyond the Moon.
Aristotle
had argued that comets were sublunary, and so didn't
violate the immutability of the Heavens.
See the figure below
(local link /
general link: great_comet_1577.html).
Tycho also showed that the comet's orbit took it through the
celestial spheres---those
celestial spheres
that
carry the planets.
He concluded the celestial spheres did
NOT exist.
They were published, however, in books that were known to
European
astronomers.
That Tycho's disproofs were
NOT widely accepted, except by
astronomers,
is reasonable.
There are many claims in science and other fields that are made
and never verified.
Often you have to wait until the issue matures.
Aristotelian cosmology, however, was beginning to shake
on its foundations.
The last great achievement of Tycho's to
mention is the introduction of
the Tychonic system.
The Tychonic system is the
Copernican system
turned on its head.
The figure below
(local link /
general link: tychonic_system.html)
explicates the Tychonic system.
Although Tycho
rejected Copernicanism,
his work undermined
Aristotelian cosmology
and the
Ptolemaic system.
Thus, he effectively
advanced Copernicanism.
The Tychonic system
provided a only temporary refuge for some against the onslaught of rampant
heliocentrism.
Tycho's own protege
Kepler---though
personally loyal to Tycho---NEVER wavered
from the path of Copernicanism.
php require("/home/jeffery/public_html/astro/tycho/tycho_wall_quadrant.html");?>
Tycho's disproofs of
Aristotelian cosmology were only verifiable
by a few other astronomers, and so most of the scholarly world could
and did ignore them.
php require("/home/jeffery/public_html/astro/supernovae/sn_1987a.html");?>
Tycho did NOT know that the
new star was a
supernova.
php require("/home/jeffery/public_html/astro/tycho/sn_1572_tycho_sky_map.html");?>
For an animation
of SN 1572,
see
Birth of the Tycho Brahe's 1572 supernova remnant | 0:45
in Supernova videos
below
(local link /
general link: supernova_videos.html).
php require("/home/jeffery/public_html/astro/supernovae/supernova_videos.html");?>
EOF
php require("/home/jeffery/public_html/astro/tycho/great_comet_1577.html");?>
php require("/home/jeffery/public_html/astro/tycho/tychonic_system.html");?>
Form groups of 2 or 3---NOT more---and tackle Homework 4 problems 18--22 on Medieval Islamic astronomy, Medieval European astronomy, Renaissance astronomy, and Nicolaus Copernicus (1473--1543).
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
php require("/home/jeffery/public_html/astro/tycho/tycho_kepler_statue.html");?>
Kepler, unlike Tycho,
was a convinced Copernican from his college
days at Tuebingen
(graduated 1591):
Kepler did NOT have the right physics although he tried to find it. But he did have one correct guiding physical principle: the distance from a planet to the Sun is the key variable in determining the shape of the orbits and the motions.
So it is NOT true to say that Kepler's discoveries were mere empirical fits to the data.
Kepler's discoveries did take a lot of calculations. See the figure below (local link / general link: kepler_work.html).
Kepler's most important discoveries are
his 3 laws of planetary motion:
Kepler derived these laws semi-imperically
by fits to Tycho's data.
But only semi-imperically.
He was guided by his theoretical
heliocentrism
and his theory that the
Earth-Sun
distance as it varied in time was a key factor as indeed it is.
Note the
3 laws of planetary motion
are all based on
heliocentric solar system model.
Isaac Newton (1643--1727)
was later able to purely theoretically derive
Kepler's 3
laws of planetary motion
from Newtonian physics.
Kepler's 3
laws of planetary motion are:
Kepler's 1st law
as we now know is a consequence of the
inverse-square law
nature of gravity which is part of
Newtonian physics.
Note that
epicycle models are dismissed
and so are
circular orbits as a GENERAL rule.
Kepler's 1st law
is illustrated in the figure below
(local link /
general link: sun_planet.html).
Kepler's 2nd law
is illustrated by the animation
in the figure below
(local link /
general link: kepler_2nd_law.html).
Kepler's 2nd law
permitted Kepler and his followers to
accurately calculate the motions of the
planets.
The calculations were tedious.
Also, the solid
celestial spheres of
Aristotelian cosmology
are mostly gone---but NOT quite.
Oddly enough, Kepler
did NOT make the mental leap to a large or infinite
universe with
stars spread throughout
space.
He retained the Aristotelian
celestial sphere of the stars
(see Wikipedia:
Celestial spheres: Renaissance)---perhaps like
The Astronomer
in the figure below
(local link /
general link: vermeer_astronomer.html).
We all live a bit in the past
and in the future,
but it was poignant to notice this tendency strongly marked in the
pioneers of the
Scientific Revolution (c.1543--c.1687).
Kepler used his
3 laws and
Tycho's
data to create his own full model of the
Solar System.
The planets
have elliptical orbits
with the Sun at
one focus
of the elliptical orbits.
The Sun is at the physical center
though NOT
at the exact geometric center of the
elliptical orbits.
Kepler's model is a modernized
heliocentric solar system model.
Kepler
summarized his discoveries in the
Epitome of Copernican Astronomy (1615--1621)
and his tables for astronomical calculation
in the Rudolphine Tables (1627)
(named for his patron the
Holy Roman Emperor
Rudolf II (1552--1612, reigned 1576--1612))
based on
Kepler's 3 laws of planetary motion
and Tycho's data.
The Rudolphine Tables
allowed the calculation of the
most accurate ephemerides ever achieved up to that time.
Now Kepler's discoveries did
NOT prove heliocentrism.
Geometrically, his models are consistent with both the
geocentric
Tychonic system
(a modernized Keplerized
Tychonic system)
and
heliocentrism.
You just had to make decision which point to take as the origin:
Earth
or Sun.
But the Earth obeys the
3 laws just like a
planet if you take it
to be a planet.
If you take the
Earth to be center of a
Tychonic system,
then you have a double system with the Sun as secondary center.
The physical explanation of the latter arrangement would have to be
more elaborate than of the former.
Nowadays, we'd call the latter arrangement an implausible
ad hoc hypothesis.
Why should the huge Sun
(which was known to be much bigger than the
Earth as
Jupiter is much bigger
than the Galilean moons)
dominate all the
planet motions, but
then in turn be dominated by the tiny Earth?
It didn't seem physically reasonable to Kepler
and eventually to NO ONE.
Recall, the Galilean moons strongly
suggested the smaller
astronomical objects
orbit the larger
astronomical objects.
Caption: The Alien's new love.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Kepler's discoveries
with their rational interpretation from the
perspective of heliocentrism
and the
accuracy/precision of the
Rudolphine Tables
did EVENTUALLY help to convince many people
that heliocentrism was probably the right physical system even though
the right physics had NOT yet been discovered.
See the adjacent figure.
Note the word "EVENTUALLY". Kepler's work in
mathematical astronomy
was inaccessible to many---particularly those steeped in
Aristotelianism.
Thus, his impact on the
Copernican revolution in his lifetime was limited.
Galileo's telescopic discoveries
would have a much more dramatic and
immediate impact as we will see below
in subsection
Galileo and the Telescope.
Another statue of Kepler is
shown in the figure below
(local link /
general link: kepler_statue_prophet.html).
How did Kepler (1571--1630)
and Galileo (1564--1642) interact?
They were nearly exact contemporaries after all and they
are considered the two most representative
scientists of the
Scientific Revolution (c.1543--c.1687)
of the 16th
and 17th
centuries.
But they NEVER met: Kepler
NEVER got south of the Alps
and Galileo NEVER north of them.
They corresponded on two occasions, but NEVER had a complete meeting of minds.
To explicate:
Galileo
NEVER absorbed Kepler's prime work
(i.e.,
Kepler's 3 laws of planetary motion)
and he may NEVER have read any of
Kepler's
important books
which were all published before
1627
and all openly advocated
heliocentrism.
Galileo may have understood
Kepler's 3 laws of planetary motion
and the other important results of
Kepler, but he NEVER used them.
Why?
We can only speculate.
After 1616, when
Copernicanism
was effectively condemned as a heresy by the
Catholic Church,
it would have been impolitic for Galileo
to have openly cited Kepler,
who was an open Copernican and a
Protestant.
But even before 1616 and
in private, Galileo
made NO use of Kepler.
It's possible he distrusted
Kepler's approach to science.
Galileo was utterly unmystical:
a true heir of Aristotle, the
experimentalist
(but NOT of dogmatic Aristotelians)
and Archimedes (c.287--c.212 BCE)
(the greatest Greek physicist).
For example, Galileo
had NO belief in astrology
though he was required to teach it since, then as now, medical students
needed astrology in order
to diagnose and prescribe.
Kepler, on the other hand, was a sort of
mathematician mystic: an heir of
Pythagoras (c.570--c.495 BCE)
and
Plato (428/427--348/347 BCE).
He started out with a deep faith in
astrology though
he understood that contemporary practice was utterly corrupt.
In later life, after failing to make any progress in developing
a scientific astrology, he
seems to have become a bit cynical about it and perhaps regarded it primarily
as a funding source.
We, with the ingenuity of posterity, can see that
Kepler
and Galileo were
both working toward modern science,
but along somewhat different paths.
But that may NOT have been apparent to
Galileo who may
have thought Kepler a
fantasist.
It also has to be said that as mathematician,
Galileo was NO innovator unlike
Kepler who was one of the
great mathematicians
of the
Scientific Revolution (c.1543--c.1687).
Galileo may simply NOT
have had the patience to assimilate
Kepler's discoveries
in mathematical astronomy.
As for Kepler's regard for
Galileo:
he highly valued Galileo's astronomical
discoveries, but
NEVER fully understood
Galileo's achievements in
physics
probably mainly because
Galileo did NOT get around to
publishing most of them until after
Kepler's death.
Kepler---who was a
German---died
of natural causes in
1630 in the midst of
the Thirty Years' War.
See the two illustrative figures below
(local link /
general link: gallowglass.html;
local link /
general link: kepler_portrait.html).
One often wonders if great contemporaries were even aware of each other.
Two who were certainly mutually cognizant
were Charles Darwin (1809--1882)
and
Abraham Lincoln (1809--1865)---but they probably didn't know they
were born on the same day 1809
Feb12.
But what of Johannes Kepler (1571--1630)
and William Shakespeare (1564--1616)?
It's just barely possible that
Shakespeare may have
heard of
Kepler,
the famous
Imperial Mathematician
(i.e., essentially court astrologer)
to
the Holy Roman Emperor
Rudolf II (1552--1612, reigned 1576--1612).
But Shakespeare exhibits only
very superficial knowledge of
astronomy/astrology
unlike Geoffrey Chaucer (c.1343--1400).
On the other hand,
Shakespeare's
fame in his time was almost totally local to England,
and so almost certainly
Kepler never heard of him.
But there is a connection: see the figure below
(local link /
general link: kepler_shakespeare.html).
Form groups of 2 or 3---NOT more---and tackle
Homework 4
problems 21--27 on
Nicolaus Copernicus (1473--1543),
Tycho Brahe (1546--1601),
and
Johannes Kepler (1571--1630).
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/kepler/kepler_work.html");?>
Note
Kepler's 3 laws of planetary motion
dispense with the ancient devices of
epicycles and
uniform circular motion.
Those ghosts from
the Greeks were at last
exorcized.
php require("/home/jeffery/public_html/astro/orbit/sun_planet.html");?>
php require("/home/jeffery/public_html/astro/orbit/kepler_2nd_law.html");?>
php require("/home/jeffery/public_html/astro/kepler/kepler_third_law.html");?>
php require("/home/jeffery/public_html/astro/orbit/kepler_all_3_laws.html");?>
php require("/home/jeffery/public_html/astro/art/art_v/vermeer_astronomer.html");?>
But even when Kepler
was a child
in 1576,
recall that Thomas Digges (c.1546--1595)
had moved on to a large universe
full of stars
(see local link /
general link: copernican_cosmos_digges.html).
php require("/home/jeffery/public_html/astro/copernicus/copernican_cosmos_digges.html");?>
php require("/home/jeffery/public_html/astro/kepler/kepler_statue_prophet.html");?>
See Galileo
and Kepler's contrasting
heroes in the figure below
(local link /
general link: raphael_plato_aristotle.html).
php require("/home/jeffery/public_html/astro/art/art_r/raphael_plato_aristotle.html");?>
php require("/home/jeffery/public_html/astro/art/art_g/gallowglass.html");?>
php require("/home/jeffery/public_html/astro/kepler/kepler_portrait.html");?>
php require("/home/jeffery/public_html/astro/kepler/kepler_shakespeare.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_3.html");?>
Group Activity:
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
In fact, Galileo learnt a lot about science from dear old Dad---who wanted Galileo to become a doctor and earn money---but that didn't work out.
Galileo, illustrated in a pugnacious mood in the figure below (local link / general link: galileo_ottavio_leoni.html).
php require("/home/jeffery/public_html/astro/galileo/galileo_ottavio_leoni.html");?>
He trained as a
mathematician---recall his father wanted him
to become a doctor---and
served as a professor
of mathematics
at the University of Pisa
(1589--1592)
and
University of Padua
(1592--1610)
and later
as the court mathematician and philosopher to
the Dukes of Tuscany
(i.e., the Medici) from
1610 until his death
(see Wikipedia: Galileo: Timeline).
Galileo is often cited as the single most important and most representative scientist (beating out Johannes Kepler (1571--1630) for top place) in the transition from traditional science (AKA proto-science nature knowledge) to modern science---the transition we call the Scientific Revolution (c.1543--c.1687) of the 16th and 17th centuries.
As far as yours truly can figure out, Galileo was pretty much a homebody and never went out of the Pisa-Venice-Rome triangle. The map of Italy in the figure below (local link / general link: map_italy_1494.html) is from a slightly earlier epoch than that of Galileo, but the main boundaries had NOT changed by Galileo's time.
php require("/home/jeffery/public_html/astro/maps/map_italy_1494.html");?>
Let us now go over the salient features of
Galileo's career:
Galileo is famous, among other things, for his demonstration of dropping balls from the Leaning Tower of Pisa. See figure below.
Caption: Alileo dropping balls.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Answer 1 is right.
Galileo held---eventually if not quite at the time of the dropping balls---that they should reach the ground at the same time in the ABSENCE of air drag and other complications like not exactly equal release time. You may never be able to reach the actual ideal case of no air drag and other complications experimentally, but you can approach it, and so envision it.
The process envisioning of IDEAL CASES---scientific idealization---was one of Galileo's scientific principles---one that has passed on into modern scientific work.
With scientific idealization at the beginning of analysis of a system, you do NOT worry about all the complicating secondary effects. You analyze the main effect in the ideal limit where there are NO secondary effects and then add the secondary effects as perturbations as needed to improve your understanding.
For the history of the dropping balls, see Leaning Tower of Pisa in the figure below.
Caption: The Leaning Tower of Pisa in Pisa, Italy.
The Leaning Tower was constructed over the period 1173--1372.
It began leaning shortly during construction finished and tilt was stabilized during the late 20th century and early 21th century.
The Leaning Tower is 56.67 m high at highest point (see Wikipedia: Leaning Tower) and leans 3.97%deg; from vertical at present (see Wikipedia: Leaning Tower).
The Leaning Tower is campanile, a free-standing bell tower.
It is located in the Piazza dei Miracoli (AKA Piazza del Duomo), the cathedral square of Pisa.
It is probably a myth that the story of Galileo (1564--1642) dropping balls from the Leaning Tower is a myth.
His earliest biographer and sometime assistant Vincenzo Viviani (1622--1703) reports the story without much detail (see Wikipedia: Galileo Galilei: Falling bodies).
So yours truly accepts it as true---it's NOT like the cherry tree thing.
The dropping balls was probably NOT a scientific experiment, but merely a demonstration for students and/or the public that balls of unequal mass fall in nearly exactly the same time.
The demonstration took place when Galileo was a professor of mathematics at the University of Pisa in the period 1589--1592.
The critics would always contend that the balls don't fall in exactly the same time.
Galileo's point was ideally they would. The smaller you make the effects of slightly unequal release time and air drag, the closer you approach the ideal case.
By understanding ideal cases, we make progress in science.
This idea was one of Galileo's important contributions to modern science.
Credit/Permission: ©
User:NotFromUtrecht,
2012 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Leaning Tower of Pisa (April 2012).jpg.
In pure astronomy, Galileo is most famous
for his telescopic discoveries and his advocacy of
Copernicanism.
Galileo did NOT invent the
telescope.
It was invented in
about 1608 in
the Netherlands by
eyeglass makers
(see Wikipedia: Telescope Invention).
Eyeglasses
had been invented circa
1290
in Europe
(see Wikipedia: Glasses: Invention)
and eyeglass makers
were common by the 17th century.
See the figure below
(local link /
general link: eyeglasses_history.html).
But once the idea of the
telescope was known,
you did NOT need to see an existing
telescope to build one.
All you had to do was go to your local
eyeglass maker
and ask them to build one for you or
build one yourself with for the right kind of
lenses.
Now when he heard of the invention of the
telescope,
Galileo
put his experimental skills
to work and quickly made the best in the world then available.
See Galileo and
telescope in the
figures below
(unlinked figure;
local link /
general link: galileo_doge.html).
Caption: Alileo and his telescope.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Galileo put his mind to it
and made all the great early astronomical telescopic discoveries
first or nearly first.
Certainly, he reported them first---remember it's
publish or perish---most of them
in his popular bestseller
Sidereus Nuncius (1610, in English The Star Messenger)
which overnight made Galileo the most famous
natural philosopher
in Europe.
The Sidereus Nuncius was written in
Latin so that everyone could read it.
There are vastly more stars
than had ever been seen by the naked eye.
The naked eye stars
(of which there are only about 5600 for ordinary good observing conditions: see
Wikipedia: Naked-eye astronomy)
were only a small fraction of all the stars.
The bigger the light-gathering power of the telescope the more
stars you saw.
In other words, there was no obvious limit to how many
stars there were.
See the figure below
for no obvious limit.
Caption: "European Southern Observatory (ESO)
Photo Ambassador Stephane Guisard
captured this astounding panorama from the site of
ALMA (AKA Atacama Large Millimeter/submillimeter
Array in the Atacama Desert
in northern Chile.
The 5000-metre-high and extremely dry
Llano de Chajnantor
offers the perfect place for this state-of-the-art
radio telescope
which studies the universe
in millimeter band
and submillimeter band."
(Heavily edited.)
The Moon is glaring away in the middle of the
Milky Way
and off to the left
are the Magellanic Clouds
(i.e., Large Magellanic Cloud (LMC)
and Small Magellanic Cloud (SMC))).
The Magellanic Clouds
are NOT visible north
of ∼ 20° N latitude:
they are
circumpolar objects for
∼ 20° N latitude and NOT
in a good way.
You have to click through to the high resolution image.
Credit/Permission: ©
ESO,
Stephane Guisard,
2012
(uploaded to Wikipedia
by User:Stas1995,
2013) /
Creative Commons
CC BY-SA 3.0.
Also the Milky Way
was at least partially resolvable into stars.
Previously the Milky Way was seen
just a band of milkiness on the sky as
it's name suggests---the milky road
(No-401--402).
Nothing had been proven, of course, but the idea that stars
varied in distance and NOT just in brightness and that
they were suns spread throughout a large or infinite space as
Thomas Digges (1546--1595)
and Giordano Bruno (1548--1600)
had at least partially suggested began to
seem plausible.
The planets were seen as disks when magnified rather than as twinkly
points like stars.
Planets were much different than
stars, much closer than
stars, or
both.
There were newly discovered features of the Moon.
See the figure below
(local link /
general link: galileo_moon_map.html).
The 4 largest
moons
(i.e., the 4 largest natural satellites)
of Jupiter
which we now call the
Galilean moons of Jupiter
See the figure below
(local link /
general link: jupiter_galilean_moons_collage_far.html).
Also the smaller bodies clearly orbited the larger body.
The Sun was known to be vastly bigger than
Earth.
Could a bigger body orbit a smaller body?
It began to seem as if it shouldn't.
Kepler had thought it shouldn't all along.
Also it was now possible for Earth to be a
planet and still have
a moons.
It had been argued that the Earth couldn't be a
planet since
planets don't have moons.
See Galileo's own
drawing of the
Galilean moons of Jupiter
in the figure below
(local link /
general link: galilean_moons_galileo.html).
Galileo's discovery of the
phases of Venus
was strong evidence against the
Ptolemaic system
and Aristotelian cosmology too.
See the figure below
(local link /
general link: venus_phases.html).
The Sun had spots that varied in time and were carried
and the Sun's face. The Sun was rotating.
The sunspots
proved that the Sun was NOT
an unchanging perfect sphere.
As with the Moon,
Aristotelian cosmology was shown to be wrong.
Saturn
had odd little appendages. Not until
Christiaan Huygens (1629--1695)
in the 1655
would the appendages be identified as
a ring
(see Wikipedia: Christiaan Huyghens:
Saturn's rings and Titan) which we now know is divided into the multiple
rings of Saturn.
The conclusion of all the new telescopic discoveries
was that
Aristotle was wrong and
Ptolemy was wrong.
Not just wrong in details, but wrong in essence: wrong that
the superlunary world was unchanging and perfect and orbited the
Earth only.
Aristotelian cosmology
and the
Ptolemaic system
were demolished.
Also, the idea that
Earth was
a planet as
it is in the Copernican system
was made a lot more plausible.
But, of course, NOT everyone admitted these conclusions at once.
The observations were tricky and NOT everyone had adequate telescopes.
Even when they had seen the new discoveries with their own eyes, some
dyed-in-the-wool
Aristotelians could NOT accept them.
It isn't very easy to accept that your whole cosmology is
evaporated---especially if you are getting on in years.
Caption: What math anxiety leads to.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
But the telescopic discoveries were NOT abstract mathematical discoveries
like Kepler's
(see the adjacent figure)
or hard to duplicate like
Tycho's
new star and
comet observations.
They were accessible to many people high and low.
But the telescopic discoveries did NOT prove heliocentrism.
Question: Could heliocentrism be proven to
be physically correct in circa
1610?
By physically correct, we mean showing that
the planets
geometrically orbited the Sun
AND that this structure
(i.e., the structure of the
Solar System)
was derivable from physical law: i.e., that the
planets
"physically" orbited the Sun.
The people of 1610 would have
NOT have said "from physical law": they would have said
from natural philosophy.
In 1610,
no one could prove heliocentrism
was "physically correct" in meaning given above.
One needs Newtonian physics
for that which would only come with
Isaac Newton (1643--1727).
However, both
Galileo
and Kepler
had good reasons for believing
heliocentrism was phyiscally correct.
The most convincing reasons by 1610 may be:
The modern understanding of the
Earth
center of mass
defining an
inertial frame
(i.e., free-fall frame)
and any location on the
Earth's
surface as being an approximate
inertial frame
was NOT available to
Galileo,
Kepler,
and their time.
However, Galileo
and
Kepler
were moving in the direction of our modern understanding.
Actually, even Newton
did NOT have the modern understanding of
inertial frames, but he
was close enough that no one noticed until
general relativity
was introduced in 1915
by Albert Einstein (1879--1955)
(see
Wikipedia: Inertial frame of reference: Newton's inertial frame of reference).
Actually, so much is known about the
Galileo affair
that we can only do a very short presentation with all kinds of interesting details omitted.
To begin,
the phyiscal intuition
of Galileo
and
Kepler was that
heliocentrism
would prove correct was correct as we know now.
Of course, the reasonable person of the time surveying the evidence
circa 1610--1630
might have suspended judgment as no doubt many did.
Galileo did, in fact,
in 1624
(see The Galileo Project: Galileo Timeline: scroll down ∼ 70% to year 1624)
obtain explicit personal permission from an old friend who happened to
have become Pope Urban VIII (1568--1644, pope 1623--1644)
(see the figure below:
local link /
general link: urban_viii.html) to write a book that would treat
heliocentrism favorably, but HYPOTHETICALLY
as something that could NOT be proven---this being
Urban's own opinion.
Only at the end does Galileo
in deus-ex-machina fashion revert to
the stance that heliocentrism could
NOT be proven, was just hypothetical,
and that
God
could have arranged the cosmos
in a way that was profoundly different from what
human reason and observation could discover.
Urban when he had become fully informed
about the book---already then passed by the censor
(who knew nothing about astronomy) and published---he,
Urban,
took umbrage.
He thought Galileo was taking him for a fool.
That very probably was really that
(Fantoli 2003).
(Certainly, NOT my own conclusion by the way.)
A lot is known about the Galileo affair, but
NOT the answer to this question.
Several possibilities occur to yours truly:
When you get on in years, you start thinking of yourself
sub specie aeternitatis: i.e.,
"from the perspective of the eternity."
But really once Urban had
decided to punish
Galileo, the consequences were pretty much determined.
The Inquisition doesn't acquit.
The figures below are some establishing shots
and an artist's conception of the
trial of Galileo
(unlinked; unlinked;
local link /
general link: galileo_inquisition.html).
Caption:
The Colosseum in Rome.
Credit/Permission: ©
Digital Imaging Project of Mary Ann Sullivan,
Bluffton College,
before or circa 2005 /
Free use is permitted for personal and educational purposes.
Caption: St. Peter's Square,
Vatican City, Rome.
The square was designed by
Bernini (1598--1680, Gian Lorenzo)
in 1656--1667
(see Wikipedia:
St. Peter's Square: History).
So the square
was NOT there when
Galileo (1564--1642)
was last there.
Credit/Permission: ©
Digital Imaging Project of Mary Ann Sullivan,
Bluffton College, 2005 /
Free use is permitted for personal and educational purposes.
He really had no choice: he was a faithful
Catholic and he had to think of
his family, friends, and his patron the
Ferdinando II de' Medici,
Grand Duke of Tuscany (1610--1670, reigned 1621--1670).
He could NOT embarrass and harm them by dying a condemned heretic---he
didn't want to for himself either very probably.
In modern terms, Galileo accepted
a plea bargain to avoid a worse fate.
Caption: Portrait of
Galileo (1564--1642)
in
old age---the Lion in Winter.
Credit/Permission:
Justus Sustermans (1597--1681),
1636
(uploaded to Wikipedia
by User:Phrood,
2005) /
Public domain.
For the end of Galileo (1564--1642),
see the adjacent figure
and the figure below
(local link /
general link: galileo_samson.html).
After Galileo's death there
were, of course, many continuing developments
in astronomy.
But the next big innovation in astronomy
would come with Newton: see
section Isaac Newton (1643--1727) below.
php require("/home/jeffery/public_html/astro/optics/eyeglasses_history.html");?>
Given that crude telescopes can be made just by fooling around with
a couple of lens or a lens and spherical mirror, it seems that the
telescope was discovered rather late in the day.
php require("/home/jeffery/public_html/astro/galileo/galileo_doge.html");?>
Galileo
telescopes were still
very crude instruments with much poorer optical
quality than even a cheap modern telescope.
For example, they didn't focus all colors in the same place: this
is called chromatic aberration.
Chromatic aberration
was probably a major annoyance for terrestrial observation with
early telescopes.
In early astronomical observation, it probably was less annoying since the
astronomical objects
that could be seen probably looked mostly
monochromatic, except
the Moon.
However, as anyone who works with equipment knows,
you can do a lot with a crude instrument if you put your mind to it.
Note that the
Sidereus Nuncius does NOT
openly advocate the heliocentric solar system???.
Galileo, aware of the
potential heresy accusation against
heliocentrism,
was cautious at this point in his life.
By the by
Johannes Kepler (1571--1630) was a public advocate of
heliocentrism from his college days---but he lived
in a different environment, at first Protestant
and then under the patronage
of the Holy Roman Emperor---who
was Roman Catholic, but did NOT feel
obliged to obey the hierarchy in all matters.
The main discoveries and their major implications are summarized below:
Image link: Wikipedia:
File:The Moon and the Arc of the Milky Way01.jpg.
The speculative hypothesis that the
Milky Way was
a mass of stars
unresolved to the naked eye
goes back at least to the
Presocratic philosopher
Democritus (c.460--c.370 BCE)
(No-401).
And also the stars were still unresolved. They were still point-like.
php require("/home/jeffery/public_html/astro/galileo/galileo_moon_map.html");?>
Actually, Galileo
was beaten in drawing
Moon maps.
by Thomas Harriot (c.1560--1621)
(see the figure below:
local link /
general link: thomas_harriot.html)---but
no one knew this because
Harriot never published his
Moon maps.
php require("/home/jeffery/public_html/astro/astronomer/thomas_harriot.html");?>
php require("/home/jeffery/public_html/astro/jupiter/moons/jupiter_galilean_moons_collage_far.html");?>
The moons orbited
Jupiter, NOT the
Earth nor the Sun.
The Earth was NOT
the only body that could be a center of motion.
php require("/home/jeffery/public_html/astro/galileo/galilean_moons_galileo.html");?>
php require("/home/jeffery/public_html/astro/ptolemy/venus_phases.html");?>
Science advances one
funeral at time.
---Max Planck (1858--1947)
(see Wikiquote: Max Planck).
Question: Can heliocentrism be
proven from a geometrical point of view?
Answer 3 is right
Answer 2 is right.
The great counter-argument to the above reasons was that
Earth seemed to be
at rest obviously
to all ordinary common sense
believed in since forever.
Also actually as yours truly
only learnt circa 2020,
UNLV
Prof. Maurice Finocchiaro
is a great expert on Galileo.
See
Books by
Maurice A. Finocchiaro.
But we won't delve into
Prof. Maurice Finocchiaro's lore.
Note
phyiscal intuition
is a vague entity.
Yours truly would define it as
a person's ability to estimate what must hold
in physics that is poorly understood
based on physics is well understood.
Clearly, this ability is fallible, but it is a guide to what is the promising path to truth
and is used in the simple problem solving and
the scientific method a whole lot.
Personally neither of Galileo
or
Kepler had any strong doubts about the
truth of heliocentrism.
After all, really and truly,
Aristotelian cosmology
and the Ptolemaic system
were both proven wrong in essence
in that time frame.
But some people were ignoring the proofs.
As is well known, the leadership of the
Catholic Church at that time
did NOT suspend judgment.
It must be pointed out that many in the hierarchy of the
Church were NOT
closed-minded on
heliocentrism, but they weren't the ones in charge of
orthodoxy.
Also, Galileo
had friends and admirers in the hierarchy and he considered himself
a faithful Catholic.
Note that after
the publication of the
Sidereus Nuncius (1610, in English The Star Messenger),
Galileo was
the most famous natural philosopher
in Europe---outside of
Europe
and Euopean outposts (See Wikipedia:
Age of Exploration, c.1400--c.1800), no one had heard of him, of course.
In 1616,
heliocentrism as physically real was condemned by a
Catholic Church decree
as a very close to being a heresy.
Hypothetical discussion of
heliocentrism was formally allowed though:
php require("/home/jeffery/public_html/astro/galileo/urban_viii.html");?>
Galileo's book
Dialogue
Concerning the Two Chief World Systems
was published in 1632
February.
As its title suggests, it is in the form of dialogue.
See the figure below
(local link /
general link: galileo_dialogue.html).
php require("/home/jeffery/public_html/astro/galileo/galileo_dialogue.html");?>
Galileo's
Dialogue,
in fact, is a vigorous
argument for heliocentrism.
But why did Galileo violate the spirit of
Urban's orders and only just barely kept to the
letter of them?
There was a trial before the Inquisition
for heresy in Rome in
1633
with all kinds of events and details.
In fact, we know so much about the events leading to the trial and afterward that one is danger of losing oneself
in details.
Download site:
Digital
Imaging Project's Colosseum, Rome site.
The download site gives more information.
Image link: Itself.
Download site:
Digital Imaging
Project's St. Peter's, Vatican City site.
The download site gives more information.
Image link: Itself.
php require("/home/jeffery/public_html/astro/galileo/galileo_inquisition.html");?>
Galileo was found guilty of "suspicion of
heresy" and
he submitted to the decision.
Image link: Wikipedia:
File:Justus Sustermans - Portrait of Galileo Galilei, 1636.jpg.
php require("/home/jeffery/public_html/astro/galileo/galileo_samson.html");?>
php require("/home/jeffery/public_html/astro/newton/newton_kneller.html");?>
But when Newton reached maturity in the
1660s,
he was in an already greatly evolved intellectual environment from
that of the old Galileo.
The first thing to say was that Newton lived in a Protestant environment.
In the Roman Catholic environment, Copernicanism had become effectively a heresy in 1616 as mentioned above in the subsection The Galileo Affair---a position from which the Roman Catholic Church would gradually retreat over next two hundred years (see Wikipedia: Heliocentrism: Age of Reason).
On Protestant side of the religious divide, Copernicanism somehow never developed into a religious issue.
It seems that the work of Galileo and Kepler, the telescope, and other things had largely evaporated Aristotelianism from religion. And without that support, purely Biblical objections to Copernicanism seemed far-fetched.
There was also the Copernicanism-based vortex theory of Rene Descartes (1596--1650) (see the figure below). This very bad, but alluring, theory had a profound attraction for some of the physics-minded people in that time (e.g., Christiaan Huygens (1629--1695) (see Wikipedia: Mechanical explanations of gravitation: Vortex). Some folks found Copernicanism acceptable based on this theory---it's always possible to believe a true result for a wrong reason.
Caption: Queen Christina of Sweden (1626--1689, reigned 1633--1654) (on the left) being instructed by Rene Descartes (1596--1650) in geometry.
A detail from a copy of Descartes at the court of Queen Christina of Sweden, Palace of Versailles, Versailles, France
Credit/Permission:
Pierre-Louis Dumesnil (1698 - 1781),
copy by Nils Forsberg (1842--1933),
1884
(uploaded to Wikipedia
by User:Jebur,
2005 /
Public domain.
Image link: Wikipedia:
File:René Descartes i samtal med Sveriges drottning, Kristina.jpg.
Thus, in the course of the 17th century, the overall intellectual world in Europe had changed.
Copernicanism became more and more accepted as the plausible theory.
This was true in Roman Catholic countries too, but the official position on Copernicanism made Copernicanism a tricky issue to discuss or write on.
Newton and his contemporaries in England were still being taught Aristotelianism, but he and probably others were already aware it was outdated. In fact, they may have learnt Copernicanism as soon as or before any other view of the Solar System.
Newton himself as an undergraduate at the University of Cambridge studied the new astronomy of Galileo, Kepler, and their followers.
Initially at least, he did NOT read the original work of Galileo and Kepler at all---like any good undergraduate, he read textbooks that simplified the presentation and omitted the out-of-date arguments and issues.
php require("/home/jeffery/public_html/astro/astronomer/jeremiah_horrocks.html");?>
We will NOT go into the history of
Newton's work on motion and the
Solar System
which he
first published in his
Principia (1687)---see
the figure below
(local link /
general link: newton_principia_page.html).
Newtonian physics
applies both to the terrestrial environment and to the
Heavens, and thus
united terrestrial and celestial physics which were profoundly distinct
in Aristotelian physics.
Newton
using Newtonian physics
was able to account to very high accuracy for the
motions of Solar System
and derive
Kepler's 3 laws of planetary motion.
See the
Kepler's 2nd law of planetary motion
illustrated in the
animation
in the figure below
(local link /
general link: kepler_2nd_law.html).
After Newton's work had been
assimilated
among the astronomically interested people
(which only took a few years), there were no more doubts
about heliocentrism.
The Catholic Church accepted
heliocentrism as an allowable view
in the 18th century.
An absolutely key point
about Newtonian physics
for the future development of
astronomy is
that it unified terrestrial and celestial
physics.
The unification finally made
astronomy
somewhat experimental.
For experimentation as it was in the
17th century,
see the figure below
(local link /
general link: guericke_pressure_horses.html).
But experiments on
Earth
do reveal aspects of the
physics
of outer space
the unification of terrestrial and celestial
physics.
To illustrate the unification,
Newton's cannonball
illustrates how
free fall
is the same
on Earth
as in outer space.
For Newton's cannonball,
see the figure below
(local link /
general link: newton_cannonball.html).
php require("/home/jeffery/public_html/astro/newton/newton_principia_page.html");?>
We will just say that
Newton's
three laws of motion
and his
law of universal gravitation
form the essence of very accurate, quantitative
physics,
Newtonian physics.
php require("/home/jeffery/public_html/astro/orbit/kepler_2nd_law.html");?>
Given Newtonian physics
and the Solar System bodies,
heliocentrism follows as a result,
NOT an axiom.
In the Newtonian system,
the planets are in accelerated orbits
about a relatively unaccelerated
Sun.
The Sun is approximately unaccelerated in
the approximate inertial frame
of the fixed stars---which
Newton incorrectly, but plausibly,
thought to be the
fundamental inertial frame of
absolute space.
Newton extrapolated
the Newtonian system to the
universe as whole
assuming that it was infinite or, at least, very large
and that the stars are other suns.
We can NOT do experiments on stars,
galaxies, etc.
php require("/home/jeffery/public_html/astro/orbit/newton_cannonball.html");?>
Form groups of 2 or 3---NOT more---and tackle Homework 4 problems 28--33 on Galileo (1564--1642) and Isaac Newton (1643--1727).
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
The winners get chocolates.
See Solutions 4.
php require("/home/jeffery/public_html/astro/videos/ial_0000_standards.html");?>
php require("/home/jeffery/public_html/astro/videos/ial_004_history.html");?>
php require("/home/jeffery/public_html/astro/art/art_c/chocolate_fountain_2.html");?>
php require("/home/jeffery/public_html/astro/art/art_v/vermeer_geographer.html");?>
The story shows, as advertized,
the scientific method in action: the cycle of theory
and observation/experiment that yields advance toward truer, more
general theories.
The cycle is an upward spiral in terms of content.
Of course, as mentioned in section scientific method---it's much too extended in time to be typical and most of the participants were NOT aware they were practicing the scientific method at least as a paradigm for how science should be done.
But at the end with Galileo, Kepler, Newton, and other lesser lights, one sees the modern scientific method developing in which physical theories are found adequate or inadequate by testing them against nature, NOT by seeing how they fit in an overall philosophy of the universe and/or metaphysics.
The development of the modern scientific method is a main feature, but NOT the only one of the Scientific Revolution (c.1543--c.1687) of the 16th and 17th centuries.
Philosophy and metaphysics still play a role. But describing that role is a lecture in itself---and one without consensus conclusions.
This essay is NOT part of the required reading for this lecture.
But yours truly believes that
Julius Caesar was right.
The
history of astronomy
does divide into three main epochs both from
science topic and human interest points of view.
Essentially, this path through history is the path that tracks along
the most advanced
astronomy
of its time (e.g., Tycho's) in the judgment of many.
Caption: "Guo Shoujing (1231--1316),
a Chinese astronomer,
engineer, and mathematician born in
Xingtai,
Hebei and living during the
Yuan Dynasty (1279--1368)"
(which was founded by Kublai Khan (1215-1294)).
Called the "Tycho Brahe (1546--1601) of
China" by
Johann Adam Schall von Bell
(1592--1666) (Jesuit
missionary and astronomer in China).
Credit/Permission: ©
User:Shizhao,
2006 /
Creative Commons
CC BY-SA 3.0.
What are the three epochs as yours truly perceives them:
Below I'll make an argument for the three epochs and other related issues.
But I would like to emphasize I'm making an idiosyncratic argument
and that is why I call this section of this lecture an essay.
I'd like to believe others would NOT disagree too much.
In point-form, the argument is as follows:
Why is the first epoch from the remote and misty beginnings in
prehistory
to circa 1700?
This is the history of astronomy
to Isaac Newton (1643--1727)
that was the topic of this lecture.
We can now see that it is essentially an astronomy of the
Solar System for two reasons.
First, actual Solar System
astro-bodies
(Sun,
Moon,
planets,
and comets
when they were thought of as being above the
ordinary air
which we call the Earth's atmosphere)
had the most complicated motions and needed the most observation and theory to explain.
The fixed stars
(which is all the stars
that anyone knew about) just sweep around once per day
(from the Earth's perspective)
on the celestial sphere
and are otherwise unchanging.
Second, for much of the time and many of the astronomers,
the fixed stars
were part of the Solar System.
They were on the outermost of the
celestial spheres
of Aristotelian cosmology.
The study of the Solar System
was often conceived of as
cosmology itself.
So there is a grand thematic unity to the astronomy epoch
prehistory
to circa 1700---it was
really cosmology,
NOT
just astronomy.
But, of course, there was a huge host of changes from
counting lunar phases
on tally sticks
(from maybe as long ago as 33,000 BCE or earlier
(see
John North 1994, The Norton History of Astronomy and Cosmology, p. xxiv;
Wikipedia: Lebombo bone)
to the Newtonian universe.
To recapitulate the epoch from prehistory
to circa 1700:
Caption: "Apollo
wearing a laurel wreath or
myrtle wreath, a white peplos
and a red himation and sandals,
seating on a lion-pawed diphros; he holds a
kithara
(a form of lyre whose
name mutated into guitar)
in his left hand and pours a libation with his right hand.
Facing him, a black bird identified as a pigeon, a jackdaw, a crow (which may allude to
his love affair with Coronis)
or a raven
(a mantic bird: see
Wikipedia: Apollo: Attributes_and_symbols).
A tondo on
an Attic white-ground kylix
attributed to the Pistoxenos Painter
(fl. circa 480--460 BCE in Athens)
(or the Berlin Painter (fl. circa 500--460 BCE
in Athens),
or Onesimos fl. 505--480 BCE
in Athens).
Diameter 18 cm (7 in.).
From a tomb (probably that of a priest) in
Delphi.
Delphi Archaeological Museum,
Inv. 8140, room XII." (Slightly edited.)
Apollo was the god of the
Sun,
poetry,
prophecy,
the plague
and many other things too.
The ancient Greeks had another
Sun god,
the Titan
Helios.
Apollo and
Helios were somewhat
syncetized.
Credit/Permission: ©
User:Fingalo,
2007 /
Creative Commons
CC BY-SA 2.0.
The theoretical understanding of
Babylonian astronomy,
aside from mythological understanding, is unknown and perhaps was meager or non-existent.
In observational technique, it doesn't seem to have surpassed
Babylonian astronomy.
On the theoretical side, there were two interconnected traditions both of which
tracked into a geocentric picture of the universe.
One tradition was that of philosophical astronomy of which the dominant theory
became Aristotelian cosmology.
We can see
that epicycle models
were all mathematical decompositions of the planetary motions
that had little physical content and that there could be no uniquely good
epicycle model
for the Solar System.
Ptolemy must have grasped the
lack of uniqueness to some degree, but hoped that his own
epicycle model
was the best, and therefore truest.
We can see that this was a mistake.
Other epicycle models
as good as his could and were built over the next 1300 years.
The two traditions were NOT completely separate.
Philosophic astronomy did try to match observations qualitatively, but
simply deferred to mathematical astronomy
in matters of exact astronomical prediction.
Mathematical astronomy (as embodied in
Ptolemy most obviously)
attempted to reconcile itself with
Aristotelian cosmology,
but NOT could derive
epicycle models from it.
But the two traditions were certainly NOT really consistent and that became a
recognized deficiency as the centuries rolled on to
Nicolaus Copernicus (1473--1543).
There was some improvements in observational and mathematical techniques.
On the theoretical side, there was virtually no progress other than cumulative
result that there was no uniquely good
epicycle model.
Both Aristotelian cosmology
and epicycle models
were swept away---NOT without a bit of a fight.
But at first without any adequate replacement.
Then came with Newton
who was able to explain the
Solar System
quantitatively by exact physical laws that
were also the physical laws of the terrestrial environment.
He took the initial conditions of the
Solar System
as givens.
In the century or so leading up to
Newton,
it had become very obvious that the
universe
was probably vastly bigger than the
Solar System
and that the fixed stars
were other suns and so could have their own
planetary systems.
So having climbed a mountain, humankind
found another larger mountain beyond.
And humankind
(as embodied in astronomers) had to ask itself what determined the structure of the
universe
as a whole and did it evolve.
It seemed obvious to try to extrapolate
Newtonian physics
to the universe.
But this did NOT lead to instant success.
In unpublished work,
Newton
tried to construct a physically consistent STATIC MODEL of
the universe---using
Newtonian physics,
of course
(see
John North 1994, The Norton History of Astronomy and Cosmology, p. 376).
He failed and rested.
Historically, that data and theory took time to accumulate starting from the
plateau of the Newtonian universe.
So certainly it is fair to regard the establishment of
Newtonian universe as the
end of the first main epoch of astronomy.
Having defined the first epoch of astronomy as a phase
of cosmology,
one now has to justify why cosmology
is so important.
Humankind
is concerned with its own meaning and nature and with that
of the universe that supports it.
That seems to be intrinsic.
The study of the universe on the
grandest scale is
cosmology.
So cosmology is
and has arguably always been an intrinsic vital concern of
humankind.
Modern astronomers usually---but NOT always---stay away from
"meaning" and stick to "nature".
It's just hard to draw anything but idiosyncratic ideas about
the meaning of the universe
from scientific cosmology.
But it has to be admitted that "meaning" probably hovers somewhere in the
unexpressed concerns of astronomers.
I think astronomy---beyond purely practical applications in timekeeping,
navigation, and
historically astrology---is supported by
humankind
because of humankind's
concern with cosmology and one other
important topic, extraterrestrial life---which
we'll get to below.
Why are other non-practical fields of astronomy
outside of
cosmology
and extraterrestrial life
supported.
Well those are fields all interlock with
cosmology
and extraterrestrial life,
and that is generally understood.
Now what of extraterrestrial life?
Why is that a vital concern of humankind?
Yours truly thinks it comes back to meaning and nature again.
To humankind, life is an intrinsic vital concern.
The universe would definitely seem
barren and meaningless without life.
And there would be no one to have vital concerns without life.
Since life in general is a vital concern,
so is life beyond the
Earth.
As cosmology has enfolded over
history, the realm beyond the Earth
was found to be bigger and bigger reducing Earth
to a pinprick.
This makes the role of
extraterrestrial life bigger and bigger.
The concern with
extraterrestrial life prompts
three age-old questions:
But I think the potential for those concerns to arise has always been there.
Intrinsic to our nature I'd say.
How do the extraterrestrial life concern
fit into the first epoch of astronomy?
Well I think there is a unifying story here too.
It seems generally the case that for most of history,
life in the Heavens
was mythological:
anthropomorphic gods
and some non-anthropomorphic gods too I suppose.
Even in religions where the
Heavens---that thing you see in the sky---were
NOT essentially the theological Heaven,
there was for a long time a tendency to view it that way as in
Dante's
Divine Comedy.
However, as the Heavens
or outer space
began to seem more like a physical realm, NOT unlike
Earth,
the idea---nowadays called cosmic pluralism
(according to our own supreme authority Wikipedia)---could
develop that there might be physical beings there
that were NOT of religious significance---that are NOT directly aware of us or
our concerns---just as we are NOT directly aware of them.
Cosmic pluralism could
NOT easily develop in
Aristotelian cosmology
where from the Moon outward
was the realm of gods or later angels.
However, there may have been some
cosmic pluralism
since Thales (c.624--c.546 BCE)
and certainly since
the Greek atomists
Leucippus (first half of 5th century BCE and
Democritus (c.460--c.370 BCE)
and their followers.
And cosmic pluralism
never entirely went away after that, but it probably seemed just a by-product
of certain philosophical systems that were NOT widely accepted.
However, when heliocentrism
made Earth
a planet
and the stars
became probably other suns with their own
planetary systems,
cosmic pluralism
became an almost inescapable probability---unless ruled out on some
philosophical basis.
In the last phase of first epoch of astronomy, that was the position reached.
Of course, there was no empirical evidence for
extraterrestrial life:
therefore was just the nearly inescapable hypothesis it must exist.
It could only be investigated in
science fiction which it
was starting with
Kepler's scifi novel
Somnium (published
posthumously in 1634) about a trip to the
Moon and
the Selenites (Moon beings
But science fiction
was virtually all that could be done for a long time.
The study of extraterrestrial life
had reached a plateau just as cosmology had.
Yours truly argues that the discovery of the Newtonian
universe
and the arrival at the nearly inescapable hypothesis
of extraterrestrial life
(or cosmic pluralism)
marks a logical end for the first main epoch of astronomy.
The story from misty beginnings to that point is a unity.
From misty beginnings, humankind
arrived NOT at final knowledge, but at new platform.
There are two other unities of the first epoch that can be mentioned too:
Circa 1700 can be considered the
end of that transformation story too.
And, of course,
astronomy
was always involved in that transformation with frequently a starring role.
In particular, in the
Scientific Revolution (c.1543--c.1687)
(roughly 1500--1700),
it had a starring role from
Nicolaus Copernicus (1473--1543)
to Newton.
Independent of astromony qua
astronomy, this second unity is of compelling intellectual interest.
It just seems to us that those times and people have become legendary to us:
part of the general modern cultural inheritance and paradigms of the
human condition.
For the human condition,
see the figure below
(local link /
general link: rodin_burghers_calais.html)
That is why it is included in
Introductory Astronomy Lectures (IAL).
The vital concern of
extraterrestrial life
is NOT a big theme of the first epoch, and so is NOT covered
for the first epoch, except in the discussion given in this section of the
lecture on history of astronomy to
Newton.
Yours truly made a big deal of it in this section because it became inescapable
to discuss what the other vital human concern was.
Why is the second epoch from circa 1700
to circa 1900?
As argued above, astronomy and
humankind had
arrived at a plateaus in the vital concerns of
physical cosmology
and
extraterrestrial life.
But the "plateau" metaphor has to be modified to slowly rising slope.
At least, subjectively to yours truly, it seems slowly rising compared to
the 1500
to circa 1700
and the period since circa 1900
compared
in advancing the vital concerns of
physical cosmology
and
extraterrestrial life.
Many new astronomical discoveries were made: e.g.,
new planets (Uranus
and Neptune),
asteroids,
and
spiral nebulae
(which in the 20th century
were discovered to be spiral galaxies).
Advances were made in the tools of discovery.
To name only the most obvious, there were
vastly improved telescopes,
photography,
and spectroscopy.
But a physically-consistent
theory of the universe
was lacking
and the existence of
other galaxies
outside of the Milky Way
was NOT known though some people thought there were.
Now it is certainly
presentism
to regard the epoch 1700
to circa 1900 just as preparation.
But to regard it as preparation from the point of view of progress on the
two vital concerns seems OK.
Because it was an epoch of preparation rather than advance on the vital concerns,
the second epoch is just less interesting to people in general.
This conclusion by yours truly seems to be pretty general.
It applies to astronomers as much as anyone else.
It is true to say that only those who are interested in the
history of astronomy
for its own sake apart from the two vital human concerns are deeply
interested in the second epoch.
Of course, astronomers do know a lot of bits and pieces of it of the
history of astronomy
in the second epoch.
One way or another, one just picks up lots of those bits and pieces
if one is immersed in astronomy.
The
Introductory Astronomy Lectures (IAL)
only covers a few bits and pieces since yours truly can't imagine the ordinary intro astro student
having much interest.
Why is the third epoch from circa 1900
to the present?
Starting circa 1900
and continuing to the present,
tremendous progress has been made on the vital concern of
cosmology.
We discuss that progress in IAL 30: Cosmology which
besides being an introduction to modern
cosmology also
covers its history.
What of the other vital concern,
extraterrestrial life.
Well from
circa 1900 to
circa 1960 most of the
progress was only in science fiction.
But that's NOT negligible: it's been the inspiration of
the huge research done on the subject since both for the general public and
astronomers---many (most?) astronomers grew up reading tons
of scifi and watching
scifi films
(2001: A Space Odyssey (1968),
Aliens (1986))---yours
truly reached saturation as a teenager and has hardly read it since.
The history of the subject of
extraterrestrial life
is NOT much covered in
Introductory Astronomy Lectures (IAL).
We can't do everything and it may NOT be of general interest.
We do cover the Martian canals
story in IAL 14: Mars: The Red Planet---it just part of the lore
of Mars---the
Martian canals don't exist, but
we are still wishing they did---and are hunting for every scrap of evidence for
Water on Mars.
We might cover some other bits and pieces.
The present-day search for
extraterrestrial life
is covered in IAL 18: Exoplanets & General Planetary Systems---well
whenever that part gets written.
The
search of extraterrestrial intelligence
(SETI) is covered in IAL 31: Intelligent Life in the Universe.
See just-for-fun figure below
(local link /
general link: ufo_new_jersey.html).
So much for the past, what of the future of astronomy?
This is an invitation for vague speculation.
Three vague, non-exclusive, possibilities occur to yours truly---just following the whole
herd of scifi---that apply to all
science including astronomy:
None of the above possibilities seem likely anytime soon.
A present, there seems no plausible way to elucidate them---maybe in
science fiction---or maybe NOT even there.
php require("/home/jeffery/public_html/astro/art/art_j/julius_caesar_tusculum_like_3.html");?>
The history of astronomy
is divided into three parts.
The history of astronomy
can be divided into many different periods in many different ways.
---Julius Caesar (100--44 BCE),
On the Gallic War
(before circa 44 BCE), quoted from memory.
For Caesar, see the adjacent figure
local link /
general link: julius_caesar_tusculum_like.html).
php require("/home/jeffery/public_html/astro/art/art_j/julius_caesar_tusculum_like.html");?>
An immediate qualification is that I mean
history of astronomy
that tracks through
prehistory
(archaeoastronomy),
ancient Mesopotamia
(Babylonian astronomy
and precursors),
classial antiquity
(Greek astronomy),
Middle Ages
(Medieval Islamic astronomy,
and Medieval European astronomy),
early modern Europe
(early modern astronomy),
and the
modern world
(modern astronomy).
php require("/home/jeffery/public_html/astro/tycho/tycho_wall_quadrant.html");?>
It leaves aside other historically interesting astronomies
(e.g., Chinese astronomy
and Mayan astronomy),
whose contributions to
modern astronomy
are limited.
Image link: Wikipedia:
File:Guo Shoujing-beijing.JPG.
Newton's achievement
did NOT,
of course, end the story of astronomy.
Image link: Wikipedia:
File:Apollo black bird AM Delphi 8140.jpg.
php require("/home/jeffery/public_html/astro/ptolemy/ptolemy_armillary.html");?>
The other tradition was one of exact
mathematical astronomy
based on
epicycle models
which culminated in the work of Ptolemy.
php require("/home/jeffery/public_html/astro/newton/newton_principia_2b.html");?>
A lot more data and theory were needed.
php require("/home/jeffery/public_html/astro/astronomer/enrico_fermi_question.html");?>
The vital concerns of
cosmology
and extraterrestrial life
have, of course, NOT always been evident in individuals or in societies.
Yours truly believes that it is because the first epoch is deeply concerned with
cosmology, a vital human concern
and has the three unities cited above that it has often been
considered a suitable topic for introductory astronomy courses.
Of course, in other areas progress was really rapid:
the Industrial Revolution,
the Enlightenment,
the progress of science in general,
the progress of astronomy
in the non-vital-concern sense,
the beginning and spread of
modern democracy
and modern nationalism,
and all the other transformations that fill volumes.
From a modern perspective, yours truly views this epoch of the
history of astronomy
as one of preparation for the third epoch where rapid progress in the
vital concerns resumes.
So on the "mountain beyond the mountain",
humankind
had NOT climbed very far by 1900---but
the real ascent was about to begin.
And the subject of extraterrestrial life
seemed stalled, except for a little science fiction
(mostly toward the end of the epoch due to
H. G. Wells (1866--1946))
and the fabulous wrong theory of intelligent life on
Mars as evidenced by
the
Martian canals (which turned out to
be non-existent).
In particular, we do cover the slow development in
cosmology
in the second epoch in
IAL 26: The Discovery of Galaxies
and we also brieflycosmology
recapitulate the whole history of
IAL 30: Cosmology.
There are specialized sources for those that do want to know the detailed
history of astronomy in
the second epoch
(e.g., John North, 1994, The Norton History of Astronomy and Cosmology).
php require("/home/jeffery/public_html/astro/art/art_u/ufo_new_jersey.html");?>