A History of Astronomy:
The Principles of Celestial Motion

Tracing the history of astronomy at least from the time of the ancient Greeks following Aristotle (384 – 322 BC), through to the early work of Ptolemy (100 – c.170 AD) up to Copernicus (1473 – 1543 AD), it is sad to say that on the whole, the entire subject was in a very sorry state. One man however, arriving on the scene shortly after Copernicus, changed everything: Johannes Kepler (1571-1630 AD)*

A Revolution in Astronomy

The scientific discoveries that were made by Kepler mark him out as one of the giants of our modern age. Indeed, without them, modern astronomy would not even exist in its present form. To understand the importance of his discoveries, it is necessary to see how his work overturned the flawed astronomical theories and models of those who came before him.

What follows then are two essays concerning the history of astronomy, the first of which details the foundations of astronomy and celestial motion as understood from the time of Ptolemy to Copernicus, and the second, the discoveries purely of Kepler, and of how he corrected the errors of his predecessors:

Ancient Astronomy: Ptolemy to Copernicus (100 - 1543 AD)


Astronomy beyond the Renaissance: Johannes Kepler (1571 - 1630 AD)

If the ancient civilisations of the past were once possessed of advanced knowledge, which itself was then subsequently lost at some remote point in history, it stands to reason that what we would consider to be the progress of our modern age, has been nothing more than the mere rediscovery of the various elements of the lost science of our predecessors.

In this statement, there is much truth. And most especially in the realm of astronomy.

For indeed, it is of great interest to note that the discoveries made by Kepler at the beginning of the modern age, provide a solution to one of the most enduring mysteries of the ancient world. Namely, the belief that the earth itself once possessed a year of exactly 360 days about the sun; such in fact being responsible for the decision by modern geometers to split up the circle into 360 equal parts (for angular analysis), which we call degrees.

Of course, though most historians who have studied the actual history of astronomy would not deny that the degree unit of angular measure was originally based upon the ancient belief in a once existent 360-day earth orbit, almost all do indeed deny that such an orbit ever truly existed in the history of the earth. Present day observations clearly show the duration of a year to be close to some 365.2421897 days**, and scientists of the current age seem quite convinced that at no point in the past has the earth undergone an increase in its orbit from the stated ancient ‘ideal’ to that of its present. A major disagreement thus exists between the civilisations of extreme antiquity and modern scholars.

The question that confronts us then is who is right? Fortunately, there is an answer to this question; found to be contained in the revolutionary discoveries in celestial mechanics that came after Copernicus.

The two basic essays above thus provide an important primer towards understanding the proof of a once existent earth year of 360 days. However, for those amongst you who may wish to skip through what may be considered by some to be a set of overly lengthy essays, you may of course go direct to the proof detailing the ancient ideal earth year, by accessing the navigation bar to the left. For under the relevant section, the essays containing the proof provide a brief summary of Kepler’s work such as is just sufficient in order to understand the proof itself, without presenting the more detailed history of astronomy over the past 2500 years, as is contained in the two essays above.

This being said, this author would himself very much urge you the reader to avail yourself of the above two essays, for they are truly informative of the basic history of astronomy as a subject, since antiquity, and most definitely will be a source of enlightenment to be sure.

References:

*The dates given for the lives of the 4 men listed are taken from “The Astronomy Encyclopaedia” (General Editor: Patrick Moore) Published by Mitchell Beazley, 1987

**The length of the earth tropical year is cited from “Explanatory Supplement to the Astronomical Almanac” (Edited by P. Kenneth Seidelmann, U.S. Naval Observatory, Washington, D.C.) Published by University Science Books 1992

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Further Reading

For a good introductory essay concerning some of the more basic aspects of astronomy from very early times, one may consult the following article on the history of astronomy.