Stonehenge as it remains. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Stonehenge as it remains. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Oh when thistle bursts and cicada,
hid in his tree, shrill and timeless,
sings his song---timeless,
then summer swoons and goat is fat
and wine is good, and maids are riggish,
but burnt are streams and men---burnt dry
by Sirius teaming with the Sun---but I
in the Dog days love a rocky shade
and Biblos from the vine.
---Hesiod,
circa 8th century BCE (freely paraphrased by the
author of these lectures from
We-77).
In many cases, perhaps most they probably did not directly worship celestial phenomena, but regarded these phenomena as established by the gods or the realm of the gods.
The ancient Babylonians for example certainly took a keen religious interest in astronomy and believed the heavens were under the power of the gods, but they did not regard celestial phenomena as gods or even even believe that it was the main home of the gods. They principally thought their gods were manifested by divine images maintained in city temples (Op-???).
Medieval Christianty certainly had a strong tendency, reinforced by Aristotelianism, to regard the observed heavens as part of the literal heaven. Dante gives the famous retelling of this view in his Divine Comedy. (Yours truly made it through Hell, but hasn't yet attempted Purgatory or Heaven).
Early people particularly conscious of signs from the gods. The behavior of birds and the entrails of sacrificial animals were particularly popular regions to look for such signs at least in the Mediterranean and Near Middle Eastern worlds. But celestial signs have always had particularly resonance and their is a tradition that they were aimed primarily at royalty and rulers.
With horoscopic astrology, astro-divination became democratized: the stars determined everyone's character and partially at least influenced their activities. Because most celestial events are regular, but come in a multitude of combinations, astrology could develop a vast realm of possibilities for imaginative astrologers. The exact influences are easy to identify---Venus in your astrological sign isn't hard to read---but giving the influences their exact weight is where the art of the astrologer was needed.
Astrology tended to become read as a science based on automatic effect and cause and less as direct messages from the gods. But direct messages could still occur. Irregular events like comets were considered particularly ominous.
Comet Ikeya-Seki, 1966 (credit: Roger Lynds/NOAO/AURA/NSF)
When beggars die, there are no comets seen;
The heavens themselves blaze forth the death of princes.
---Calpurnia, Act 2, Scene 2,
Julius Caesar, Wm. Shakespeare
In Shakespeare's time comets were still often considered literal signs. To this day, the LONG-HAIRED STARS evoke some misgiving especially as a collision with one would be disastrous.
Astrology is still with us: it's only a click away to your horoscope. There have always been DISSENTERS, of course:
Men at some time are masters of their fates:
The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings.
---Cassius, Act 1, Scene 2,
Julius Caesar, Wm. Shakespeare
They usually come to a sticky end.
Question: Where on the Celestial Sphere is a body that rises due east?
It's ``on'' Remember the Earth is a point compared to the Celestial Sphere. So anything on the Celestial equator will be on a plane perpendicular to the Celestial Axis which is also just the Earth's axis. Thus the object will be due east if it is crossing the eastern horizon any place on Earth.
A physical map of the British Isles. Stonehenge is in southwest England on the Salisbury Plain.
Stonehenge from a distance. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Stonehenge at closer range. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Stonehenge as it remains. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
The Heelstone of Stonehenge. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
The structure to the left could be a portable---which just goes to show how advance the Stonehengers were.
This is a very crude, schematic map of Stonehenge. I drew it all myself. But you see the Heelstone off to the northeast along ancient avenue. At the Summer Solstice the Sun rises over the Heelstone as seen from the Altar Stone. This is the fartherest northward point that the Sun reaches before heading south again.
There are many other astro alignments at Stonehenge that can be found when viewing the horizon from the Altar Stone.
More extravagant claims of astronomical function are certainly false: e.g., that Stonehenge was an analog computer used to calculate eclipses (Av-71).
The Pyramids at Giza from circa 2500 BCE. They make you wonder about people who build absurd structures in the middle of the desert. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
The faces of the Pyramids are aligned with the cardinal directions: north, south, east, west.
There may be other astro-alignments built into the pyramids (No-9).
They wrote on clay.
Cuneiform tablet: a receipt for 5 sheep. Credit: material adapted from ``Cuneiform Inscriptions of the University of Minnesota Libraries web site ; Reproduced by permission for 2003/2004 academic year; download site: UM 5)
The Babylonians used sexagesimal number system for mathematics and astronomy. They used the sexagesimal system consistently only for these purposes (Ne-17). They used other systems including the ubiquitous 10-based system in other contexts usually. The 10-based system is common: everyone counts on their fingers. A 20-based system may means you are down to your toes.
Question: If ``1'' is used to represent a 60-base, what in ordinary base 10 is ``11'' in base 60?
The Babylonians new the Pythagorian theorem (Ne-36) and how to solve quadratic equations (Ne-41) before circa 1600 BCE.
Mind you they didn't have the compact notation we have and they didn't understand the concept of using symbols to represent unknowns.
Venus tablet copy. Credit: ancient astronomers and copyists; modern credit: Langdon et al. (1928) (believed to be public domain).
The original Venus tablet from which many copies were made dates from circa 1600 BCE.
It shows that the Babylonians as early as that could rely on cycles to make relatively accurate predictions.
Most solar system motions repeat if you wait long enough. Venus' motions relative to the fixed stars and the Sun repeat approximately about every 8 years (No-29). The Venus tablet exhibits this knowledge.
You can build up cycles for the other planets and for eclipses. Eclipses repeat approximately about every 18 years: this is called the Saros cycle by moderns.
Thus a primitive predictive astronomy can be built up from cycles. The ancient Babylonians did this first.
In the period 400 BCE -- 100 CE, Babylonian astronomy culminated.
Question: What are ephemerides?
But we have no evidence that the astrophysics was of any interest to them: i.e., attempting to understand the cosmos in terms of physical laws and a 3-dimensional structure.
They may well have been satisfied with a dome model of the the cosmos in which the celestial objects were manifestations of the gods.
But in fact we don't know that much. Our understanding of their mathematical astronomy just comes from calculational and ephemeris tablets. There is no physical explanation or any explanation actually. All we know is that the tablets were written in priest-like surroundings.
The pattern of ``golden ages'' and stagnation seems to be typical of science in traditional science. The ancient Greeks had a golden age, and so did Medieval Islamic society. So did traditional Chinese society and Indian society---probably a few, but yours truly is not so well informed on these societies.
Part of the explanation 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 on 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 and can be built on later.
Science in modern society since circa 1600 is radically different. It is relentlessly progressive and strongly supported by society.
Ancient Greek world circa 550 BCE. Click on image for magnification and credit.
The ancient Greek world---Hellas---was more extensive than modern Greece. It included the west coast of Turkey, the littoral of the Black Sea, and southern Italy and Sicily.
The earliest natural philosophers were from Ionia (eastern Turkey): e.g., Thales, Anaximander, Anaximenes, and Pythagoras all in the 6th century BCE.
Thales, Anaximander, and Anaximenes all tried to create theories of the cosmos that were based on elementary principles without invoking anthropomorthic gods. Thales thought the basic substance was water. Anaximenes thought it was air. Anaximander thought it was the Boundless.
Pythagoras is famous for founding a sect that believed that the world is based on mathematics. This could have led to mathematical physics, but in fact led to number mysticism.
A great advance was made by Parmenides of Elea (in southern Italy). He is the first person to propose that the Earth was a sphere. He also thought that the cosmos was spherically symmetric and centered on the Earth.
His reasoning insofar as we know it seems to have been philosophical: the spherical shape would allow perfect balance and this sustained the cosmos (Fu-54--56).
But he may have had more empirical reasons for proposing a round Earth. In any case Aristotle later summarized the empirical evidence for the round Earth:
Question: As you go farther north stars close to the North Celestial Pole are:
Recall in astro-jargon, altitude is height above the horizon.
The ancient Greek theatre in Segesta, Sicily (5th century). Click on image for credit.
This is not so far from Parmenides's home town, but he'd have had to cross water to get there.
The ancient Greeks liked to have view in their theatres.
Hey, we need a bigger amphitheatre out in our esplanade.
Beyond having a round Earth, the Greeks tried to understand the 3-dimensional structure of the Cosmos from a geocentric view---which, of course, is the wrong one.
Above is a simplified version for illustration of model of Eudoxos (408--355 BCE) for explaining the motion of the Sun around the Earth.
The fixed stars are on an outer sphere---the Celestial Sphere conceived of as a real thing---and this sphere carries around the Sun sphere.
The Celestial Sphere rotates once per day.
The Sun sphere rotates once per year.
The two motions are superimposed and this accounts for the appearances.
Eudoxos' model was the first model to quantitatively explain the non-trivial Celestial motions in terms of 3-dimensional geometric structures. Much more elaborate models were needed for the planets---in particular to explain their retrograde motions.
Question: Retrograde motion is when a planet on the sky as seen from Earth moves:
The Parthenon from the west. The Parthenon is on the Acropolis of Athens. Click on image for credit.
Aristotle (384--322 BCE) established a school, the Lyceum in Athens, in order propagate what we would now call the liberal arts and sciences.
A cartoon of the Aristotelian cosmos.
Aristotle's cosmology was a development from Eudoxos' model. He used 55 spheres all concentric around the Earth to account for all the celestial motions. Beyond the outermost sphere was nothing---not even empty space---just nothing.
The celestial spheres were conceived of as real solid bodies made out of quintessence---the 5th element. But of course they couldn't be seen and so came to be called the crystalline spheres.
Aristotle (and other 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.
(In modern physics were understand why this doesn't happen. Each part of the Earth is approximately an unaccelerated frame for most purposes. Relative to unaccelerated frames, Newtonian laws of physics apply directly: e.g., in a smoothly moving train or plane. There are no strange ``forces'' unless you accelerate: speed up, slow down, or turn.)
Since the celestial bodies moved around us, the Earth was clearly at the center of the Cosmos. This is the GEOCENTRIC point of view.
Aristotle also postulated a radical distinction between Earth and Heaven. The Heavens were a realm of eternal cyclic motions of perfect bodies. Gods (or in later monotheistic versions angels) propelled the spheres.
The Earth was imperfect and changing.
In defence of geocentrism, Aristotle did note that there was no observable stellar parallax.
Galileo and other Copernicans of the 17th centuries would try to find stellar parallax. But the stars are really remote by solar system length scales and stellar parallax is minute even for the closest stars. Stellar parallax was not finally discovered until 1838 (No-419).
In later Antiquity, in Medieval Islamic and European cultures, and in the Renaissance, ARISTOTLE for many---but not all---became the highest or even the SUPREME AUTHORITY in philosophy including natural philosophy.
Aristotle seemed to offer to the 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.
In particular, Aristotle's cosmology and physics became a philosophical dogma.
In fact his, cosmology is not quantitatively correct---it's not even qualitatively correct if you look at it closely. You can't produce accurate ephemerides from his model.
Aristotelians---those pesky varmits---rationalized that Aristotle had got it right as far as human understanding could reach.
With these models he could quantitatively predict the celestial motions and, in particular, explain retrograde motions.
Although not a strict Aristotelian, Ptolemy basically followed Aristotle's physical ideas and remained a strict geocentrist.
He did admit non-geocentric models were geometrically possible, but he said they were physically absurd.
A simple epicycle model. A model like this could be construct for all the planets, Sun, and Moon.
Retrograde motion was explained by the epicycle. The two compounded motions could add up to a westward of the planet on the sky.
But there is no way to know the overall structure. The model for each object could be put at any distance in any order.
Ptolemy did actually give an order and inferred distances, but his arguments were not conclusive for other people---of course, since his models were wrong, his arguments couldn't be conclusive.
What is wrong with the Ptolmaic models? (Besides from the fact we know they arn't right.)
They arn't unique. By varying the size of the deferents and epicycles and adding epicycles on epicycles, you can create endless models that give the same predictions as Ptolemy's. And as mentioned above, there was no way to set the distances.
His models are in fact mathematical decompositions---non-unique ones.
Question: What is 7 really?
Of course, unlike 7, the solar system really does have unique structure.
For 13 hundred years after Ptolemy, astronomers in the Indian, Islamic, and European cultures would try to improve on Ptolemy's models. They found variations that were as accurate, but not really more accurate and they couldn't tell which was right.
Question: In order to break the deadlock of Ptolemaic systems and discover the true structure of the solar system you had to have:
Not much is known about Aristarchos, but he is the first proposer of the heliocentric model of the solar system.
We only know he proposed it from a few comments in surviving ancient writings.
But those comments suggest he may well have understood why heliocentrism is the key to understanding the solar system structure.
Aristarchos is a precursor. A person who discovers something, but fails to make the world appreciate it's value.
On the other hand they did improve mathematical techniques. The trigonometric functions were developed in Indian-Islamic worlds as were Arabic numerals which came replace the clumsy notations of the past: e.g., cuneiform, Greek, and Roman numerals.
With Arabic numerals the role of 10-based place value arithmetic began to dominate. A 12-based place value system might have been handier, but since our hands have 10 fingers . . .
Decimal fractions were also developed with an important treatise being written by Al-Kashi (15th century) who worked at Samarqand observatory of the Samarqand ruler Uleg Beg (1394---1449) (No-200.
The Samarqand observatory was the greatest of the Islamic observatories and produced new measurements of exceptional quality that alas proved to have little consequence on the development of astronomy---but one must keep trying.
``What is truth?'' as Copernicus may have asked.
Nicolaus Copernicus (1473--1543) was German-Polish astronomer, physician, economist, and church official and lawyer (of the Roman Catholic Church).
He studied in Italy for most of the decade 1496--1506. In Padua where he was at the university, Copernicus would have known---one assumes---the church of Sant'Antonio built circa 1290: Galileo would know it---one assumes---when he was a professor in Padua in 1592--1610.
Click on image for credit.
Question: Why did the building use arches instead of lintels (those things on the tops of doors and windows and trilithons)?
Note the answer is also why planets and stars are ROUND. Gravity overcomes shear resistance of solids, but not compression resistance which can be a lot bigger.
At the microscopic level this can be understand. It is easier to break atomic bonds that give forces that resist shear than to compress atoms to a smaller size than they want to be.
One diagram shows you why.
Given the heliocentric idea and assuming circular orbits for the planets, a little trigonometry gives you the distances in astronomical units to Venus and Mercury.
The outer planets take a little more work, but their distances in astronomical units can be found too.
Thus, the structure of the solar system is revealed:
Now the absolute distances were not known at all accurately since the astronomical unit was not known in terms of the Earth's size. Only in the 17th century would the astronomical unit begin to be estimated accurately (No-351). Copernicus' used the ancient Greek value for the astronomical unit which was about 23 times too small (No-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.
Copernicus's heliocentrism (Copernicanism) was recognized by as great theory by those astronomers who we see retrospectively as most modern and progressive: e.g., Galileo and Johannes Kepler.
In order to make a predictive model, he had to use epicycles and other ancient devices. He still used the celestial spheres of Aristotle. In fact, except for the transposition of the Earth and Sun, his models are much like Ptolemy's in mathematical construction.
One noteworthy improvement over Ptolemy was a natural explanation of retrograde motion.
So in mathematical astronomy Copernicus was not completely radical. But his model totally upset physics as it was then understood: i.e., Aristotelian physics which we won't bother to detail here.
Copernicus made the Earth a planet.
Somehow it had to carry its own frame of rest with it.
If Earth was a planet, the other planets therefore could be like the Earth.
Also since stellar parallax was not observed, the star sphere had to be extremely remote. The universe had to be big by comparison to what people had thought.
Aristotelian cosmology was totally wrong if Copernicus was right.
Thus, Copernicanism was potentially a heresy on both sides of the religious divide. Note Copernicus' life spanned the Reformation and the beginning of the wars of religion in Europe.
Copernicus was quite aware of this potential heresy problem---he was a Catholic Church lawyer after all. He tried to defend his orthodoxy of his theory by dedicating his book to Pope Paul III and addressing himself only to astronomers, not to theologians.
In fact, one of the reasons for delaying publication of his book until he was near end of his life may have been to ensure, he wouldn't be around to face awkward questions.
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.
Not an absolutely new idea, but a new idea in the context of the Copernican system.
Tycho carried out a 20 year program of observational astronomy that achieved an accuracy never obtained before particularly for the planetary motion. He used various divided circles---quadrants and the like. But it was all naked eye astronomy.
His equipment was not at all novel---in essentials it had all existed for millennia. What was novel was his commitment to reducing mechanical errors. Tycho perceived that one of the problems of astronomy was that new observations were as poor as the old ones.
To renovate astronomy you needed better observations, not just new ones.
The utility of Tycho's data comes with its use in the models of Kepler which we'll come to below.
SN 1987A in the Large Magellanic Cloud.
Modern Supernova 1987A: the bright, pointy star near the center. SN 1987A is in a dwarf galaxy the Large Magellanic Cloud that is a satellite of our galaxy. Many of the stars in this picture are foreground stars in our Galaxy. The pink region is the 30 Doradus, a bright emission region gas in the LMC. It's a star formation region. Incidentally this most famous of all modern supernovae was discovered by Ian Shelton, the brother of my UNLV colleague David Shelton.
Credit: Marcelo Bass, CTIO/NOAO/AURA/NSF .
Tycho did not know that the new star was a supernova.
But he did prove that the new star was beyond the Moon. Thus he proved there was change in the Heavens that Aristotle was wrong.
In 1577, Tycho proved that the great comet of that year was also beyond the Moon. Aristotle had argued that comets were sublunary, and so didn't violate the immutability of the heavens.
Tycho also showed that the comet's orbit took it through the celestials spheres---those crystalline spheres that carry the planets. He concluded the crystalline spheres did not exist.
Tycho's disproofs of Aristotelian cosmology were only verifiable by a few other astronomers, and so most the scholarly world could and did ignore them.
That Tycho's disproofs were not widely accepted 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.
All the astro bodies, except Earth and Moon orbit the Sun and the Sun and Moon orbit the Earth.
Geometrically, the Tychonic system is valid. If you take the Earth, as your reference point, the Tychonic system follows.
But in modern physics, the Tychonic system is not relevant. It is the mass and gravity of the Sun which dominates the motion and the Sun sets the approximately unaccelerated reference system of the solar system.
Tycho and his contemporaries did not have modern physics, of course: that would come with Newton in 1687.
But Galileo and Kepler believed that the true physics would be one in which the Sun was the physical center of solar system motion. This belief was based on their weighing of the evidence available---and, of course, they were correct---as we know now.
Many of Tycho's contemporaries felt the Tychonic system was the happy mean. The new system that was not too radical.
The Imperial Mathematician was traditionally one of court astrologer, but Kepler was given freedom to pursue novel research.
Luckily, Kepler got hold Tycho's data: Tycho's worthless heirs would have sat on them dog-in-manger style, and thus have rendered much of Tycho's work barren.
Kepler, unlike Tycho, was a convinced Copernican from his college days (Tuebingen 1591).
Using the correct theory and the best data every available he was able to find the true motions of the planets. Remember Copernicus still used epicycles and the like.
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 parameter 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.
Kepler's most important discoveries are his three laws.
Now Kepler's discoveries did not prove heliocentrism. Geometrically his models are consistent with both the Tychonic and Copernican pictures. You just had to make decision which point to take as the origin.
But the Earth obeys the three 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.
Why should the huge Sun dominate all the planet motions, but then in turn be dominated by the tiny Earth? It didn't seem physically reasonable to Kepler.
Kepler's discoveries with their comparatively elegant interpretation from the heliocentric view and the accuracy of the Rudolfine Tables did eventually help to convince many people that the heliocentric system was probably the right physical system even though the right physics had not yet been invented.
Note the word EVENTUALLY. Kepler's work in mathematical astronomy was inaccessible to many---particularly those steeped in Aristotelian philosophy. Thus, his impact on the Copernican debate in his lifetime was limited.
Galileo's telescopic discoveries would have a much more dramatic and immediate impact as we will see.
Frederick Rosenkrantz and Knud Henriksen Gyldenstierne were cousins of Tycho Brahe and part of the Danish embassy to England in 1592 where Shakespeare noticed them. He would cast them in bit parts in Hamlet.
Rosencrantz would later meet Kepler. The link between Kepler and Shakespeare is established---I knew there had to be one. They may never heard of each other---although Kepler's fame as an astrologer may have penetrated to England---but maybe only 1 or 2 degrees of separation.
He is often cited as the single most important or at least most representative figure in the transition from traditional science to modern science.
Galileo is also known for a number of scientific quarrels. He, in fact, won most of those---but in some cases only posthumously.
As far as I can figure out, Galileo was pretty much a homebody and never went out of the Pisa, Venice, Rome triangle. The map below is from a slightly earlier epoch than Galileo, but the main divisions were unchanged.
Aristotle held that qualitatively, the heavier ball should reach the ground first. And in many actual trials that is exactly what happens: e.g., paper and pen dropped. The acceleration due to gravity is mass independent as we'll see, but the acceleration (always a deceleration) due to air resistance does depend on mass and/or density in a complex way.
Galileo held that they should reach the ground at the same time in the absence of air resistance. You may never be able to reach the actual ideal case of no air resistance experimentally, but you can approach it, and so envision it.
This process of approach to and envisioning of ideal cases was one of Galileo's scientific principles---one that has passed on into modern scientific work.
At the beginning of analysis, don't start worrying about all the complications. Solve the ideal problem first and then add secondary effects to be solved as perturbations.
The Leaning Tower of Pisa from which Galileo did his famous ball dropping demonstration. Click on the image for credit.
By the way it is a myth that the Leaning Tower demonstration was a myth. Galileo's earliest biographer said he did it---without any details---so why should anyone not believe it. It was probably in the nature of demonstration for the students, not a precise experiment.
Galileo did not invent the telescope. It was invented in 1608 in the Netherlands by eye-glass makers.
In Europe, eye-glasses had been invented sometime before 1292 (Gies-227) and lens and eye-glass makers were common by the 17th century.
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.
Galileo when he heard of the telescope put his experimental skills to work and quickly made the best in the world then.
His 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.
But you can do a lot with a crude instrument if you put your mind to it. And Galileo made all the great early astronomical telescopic discoveries first or nearly first.
Certainly, he reported them first: most of them in his popular bestseller: The Star Messenger, and so overnight Galileo became the most famous natural philosopher in Europe. The main discoveries and their major implications can be summarized:
The naked eye stars (of which there are only a few thousand in fact) 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.
Also the Milk Way was at least partially resolvable into stars. Previously the Milky Way was just a band of milkiness on the sky as it's name suggests---the milky road.
Also stars were still unresolved. They were still point-like.
Nothing had been proven, of course, but the idea that stars were suns spread throughout a large or infinite space as Leonard Digges and Giordano Bruno had at least partially suggested began to seem plausible.
(To the right is Galileo's own Moon map from 1609 December 3. In the bright half is the hindquarters of the Rabbit, but I can't identify the big crater. Galileo seems to have exagerated the size of one several craters in the vicinity.)
The mountain shadows, seen most clearly at the terminator (the line dividing the bright and dark sides of the Moon), verified varying elevation occurred not just varying color (Ze-60).
The Moon was clearly a body not altogether unlike the Earth. It was not a perfect sphere as in Aristotelian cosmology.
And if the Moon was Earth-like, then the Earth was Moon-like. The argument that the Earth could not be a planet because it was unlike the celestial bodies vanished.
The moons orbited Jupiter, not the Earth nor the Sun. The Earth was not the only body that could be a center of motion.
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 Moon. It had been argued that the Earth couldn't be a planet since planets don't have moons.
Thus Venus shone by reflected sunlight like the Moon: thus perhaps it was like the Moon and Earth with mountains and geology.
The nearly full phase of Venus showed that Venus clearly passed behind the Sun.
In the Ptolemaic model, Venus orbited on an deferent that was closer than the Sun: full phases were not possible. Ptolemy was just wrong about the Venus orbit.
The Aristotelian world was demolished.
But, of course, not everyone saw that 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.
But the telescopic discoveries were not abstract mathematical discoveries like Kepler's or hard to duplicate like Tycho's new star and comet observations.
They were accessible to many people high and low.
Question Can heliocentrism be proven physically in circa 1610?
The physical sense of Galileo and Kepler was that heliocentrism would prove correct was correct as we know now. Personally neither of them had any strong doubts.
Of course, the reasonable person of the time surveying the evidence might have suspended judgment as no doubt many did.
As is well known the leadership of the Catholic Church at that time didn't suspend judgment.
It must be pointed out that many in hierarchy of the Church were not closed-minded on the issue, but they weren't in charge of orthodoxy.
In 1616, heliocentrism as physically real was condemned by a Church decree as a heresy effectively.
Hypothetical discussion of heliocentrism was allowed though.
Galileo obtained permission from an old friend who happened to have become Pope Urban VIII to write a book that would treat heliocentrism favorably, but HYPOTHETICALLY as something that could NOT be proven.
Galileo's book Dialogue Concerning the Two Chief World Systems was published in 1632 February. As it's title suggests it is in the form of dialogue among three friends: a defender of Copernicanism (Galileo's spokesman Salviati), a knowledgeable neutral (Sagredo), and an Aristotelian called Simplicio whose name is obviously suggestive.
Galileo's book in fact is a strong argument for heliocentrism---famously his favorite argument about the cause of the tides is actually quite wrong.
Galileo only at the end in deus ex machina fashion reverts to the stance that heliocentrism could not be proven 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 circulating---took umbrage.
He thought Galileo was taking him for a fool. That very probably was really that (Fan-430). (Certainly, not my own conclusion by the way.)
There was a trial before the Inquisition for heresy in Rome in 1633 with all kinds of details and events, but really once Urban had decided to punish Galileo the consequences were pretty much determined.
The Colosseum in Rome. Click on the image for credit.
St. Peter's Square, Vatican City, Rome. Click on the image for credit.
He really had no choice: he was a perfectly sincere Catholic and hardly would have relished going to the stake as an enemy of the faith.
After his trial in 1633, Galileo lived on for another 9 years under house arrest. For an elderly and infirm person, house arrest was probably not too unbearable.
And he was still famous and sought out: for example, he was visited in 1638 by John Milton (Fan-488).
Naturally he had to abandon astronomy, but he turned to summarizing his discoveries and developments in physics and engineering.
The resulting book with abbreviated title Two New Sciences had to be smuggled abroad to be published. It was printed in the Netherlands in 1638, by which time Galileo, age 74, had become blind(Fan-488).
Galileo's physics was only a half-way point to Newtonian physics, but Galileo's approach to practical engineering problems and his concept of work done by machines were more useful to engineers of the 17th and later centuries than Newton's original formulation of Newtonian physics (Ca-97).
Newtonian physics would, of course, eventually be shown to comprehend everything that was correct in Galileo's physics.
Two New Sciences was a book for the future in both theoretical and applied physics. But by implication it also relegated Aristotelian physics and cosmology to history: Samson with a last effort pulling down the temple.
Well as the 17th century progressed, it became more and more accepted as the plausible theory.
In Newtonian physics, which arrived in 1687, heliocentrism is fully explained physically. Of course, only the solar system is heliocentric. The universe is now seen as huge, perhaps infinite, and all the stars are other suns.
After Newton, among the astronomically interested people there were no doubts.
The Catholic Church quietly dropped heliocentrism as a heresy in the 18th century.
It does show the scientific method in action: the cycle of theory and observation/experiment that yields advance toward truer, more general theories. The scientific method cycle is an upward spiral, not just a circle.
Of course, the history we've gone over not a typical example of the scientific method: it's much too extended in time to be typical.
But at the end with Galileo, Kepler, and other lesser lights, one sees the modern scientific method developing.
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 metaphysics.
