An Essay on the Three Epochs of the History of Astronomy

From the remote and misty beginnings in prehistory to circa 1700.
From circa 1700 to circa 1900.
From 1900 to the present---which is a moment that keeps trying to get away from us.

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:

From the Remote and Misty Beginnings in Prehistory to Circa 1700:
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:
1. In prehistory and early history, the theoretical understanding seems to have been mostly that anthropomorphic gods ordered the universe). On the observational side, one just had casual observations and simple countings of events.
2. Alignment astronomy was developed in prehistory in many cultures and carried on into early history.
3. Exact, systematic, written-record observations started most notably in Babylonian astronomy which flourished from early beginnings (circa 1800 BCE: see Wikipedia: Babylonian Astronomy: Old Babylonian astronomy) and petered out, at least as an independent tradition, with the extinction of cuneiform script in the 2nd century CE.
  The theoretical understanding of Babylonian astronomy, aside from mythological understanding, is unknown and perhaps was meager or non-existent.
4. Greek astronomy in Classical Antiquity (c.800 BCE--c.500 CE) had its heyday in period from Thales (c.624--c.546 BCE) to Ptolemy (c.100--c.170 CE).
  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.
  The other tradition was one of exact
  mathematical astronomy based on epicycle models which culminated in the work of Ptolemy.
  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).
5. Medieval Islamic astronomy and Medieval European astronomy largely carried on the two traditions of Greek astronomy.
  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.
6. Early modern astronomy (which developed in the physical context of Europe) saw the development of heliocentrism (beginning with Copernicus, the telescopes, and the eventual triumph the Newtonian universe.
  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.
Newton's achievement did NOT, of course, end the story of astronomy.
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.
A lot more data and theory were needed.
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.
Why is Cosmology So Important?
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.
Extraterrestrial Life:
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:
1. Is there extraterrestrial life?
2. Or are we alone?
3. And "Where are they!"---which is a probably emphatic version of what Enrico Fermi (1901--1954) once said.
The vital concerns of
cosmology and extraterrestrial life have, of course, NOT always been evident in individuals or in societies.
But I think the potential for those concerns to arise has always been there.
Intrinsic to our nature I'd say.
The Extraterrestrial Life Concern in the First Epoch of Astronomy:
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.
The End of the First Main Epoch of Astronomy:
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:
1. The second unity is that the period from prehistory to circa 1700 was also the period of the transformation of nature knowledge of various kinds into modern science.
  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.
2. The third unity is that of a thrilling story that passes through the some of the great ages of humankind and that involves great brains such as anonymous Stonehengers (AKA Neolithic Britons), Democritus (c.460--c.370 BCE), Omar Khayyam (1048--1123), Johannes Kepler (1571--1630), Galileo (1564--1642), and Newton (1643--1727).
  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)
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.
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.
The Second Epoch from Circa 1700 to Circa 1900:
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.
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.
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.
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).
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.
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).
The Third Epoch from Circa 1900 to the Present:
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).
The Future of Astronomy:
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:
1. Science asymptotically reaches the limit of knowing all that we can know, but NOT all that is to be known.
2. Somehow we lose knowledge through societal collapse or absentmindness.
3. Humankind reaches a transcendent state in which we know everything.
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.