History of Astronomy From the Roman Empire to the Present, Part 2
Copernicus and Galileo
Ptolemy’s was still the astronomy of the world when Columbus discovered America, 1492, but there was living at that time— in the little town of Franenburg, in Prussia— a youth of 18, who was destined in later years to overthrow the astronomy of Hipparchus and Ptolemy, and to become himself the founder of a new theory which has since been universally accepted in its stead ; Nicholas Copernicus.
It is to be remembered that at that time the earth was believed to stand still, while the sun, moon, planets and stars moved round it daily from east to west, as stated by Ptolemy ; but this did not seem reasonable to Copernicus. He was a daring and original thinker, willing to challenge any theory— be it ever so long established— if it did not appear logical to him, and he contended that it was unreasonable to suppose that all the vast firmament of heavenly bodies revolved around this relatively little earth, but, on the contrary, it was more reasonable to believe that the earth itself rotated and revolved around an enormous sun, moving within a firmament of stars that were fixed in infinite space ; for in either case the appearance of the heavens would be the same to an observer on the surface of the earth.
This was the idea that inspired Nicholas Copernicus to labour for twenty-seven years developing the Heliocentric Theory of the universe, and in compiling the book that made him famous : ”De Revolutionibus Orbium Ccelestium,” which was published in the last year of his life: 1543.
And now it is for us to very carefully study this fundamental idea of the Heliocentric theory, for there is an error in it. Ptolemy had made it appear that the sun and stars revolved around a stationary earth, but Copernicus advanced the theory that it was the earth which revolved around a stationary sun, while the stars were fixed; and either of these entirely opposite theories gives an equally satisfactory explanation of the appearance of the sun by day and the stars by night. Copernicus did not produce any newly discovered fact to prove that Ptolemy was wrong, neither did he offer any proof that he himself was right, but worked out his system to show that he could account for all the appearances of the heavens quite as well as the Egyptian had done, though working on an entirely different hypothesis ; and offered his new Heliocentric Theory as an alternative.
He argued that it was more reasonable to conceive the earth to be revolving round the sun than it was to think of the sun revolving round the earth, because it was more reasonable that the smaller body should move round the greater. And that is good logic.
We see that Copernicus recognised the physical law that the lesser shall be governed by the greater, and that is the pivot upon which the whole of his astronomy turns; but it is perfectly clear that in building up his theories he assumed the earth to be much smaller than the sun, and also smaller than the stars ; and that was pure assumption unsupported by any kind of fact. In the absence of any proof as to whether the earth or the sun was the greater of the two, and having only the evidence of the senses to guide him, it would have been more reasonable had he left astronomy as it was, seeing that the sun appeared to move round the earth, while he himself was unconscious of any movement.
When he supposed the stars to be motionless in space, far outside the solar system, he was assuming them to be infinitely distant; relying entirely upon the statement made by Hipparchus seventeen hundred years before. It is strange that he should have accepted this single statement on faith while he was in the very act of repudiating all the rest of the astronomy of Hipparchus and Ptolemy, but the fact remains that he did accept the ” infinitely distant ” doctrine without question, and that led him to suppose the heavenly bodies to be proportionately large; hence the rest of his reasoning’s followed as a matter of course.
He saw that the Geocentric Theory of the universe did not harmonise with the idea that the stars were infinitely distant, and so far we agree with him. He had at that time the choice of two courses open to him:—he might have studied the conclusion which had been arrived at by Hipparchus, and found the error there ; but instead of doing that he chose to find fault with the whole theory of the universe, to overthrow it, and invent an entirely new astronomy to fit the error of Hipparchus!
It was a most unfortunate choice, but it is now made clear that the whole work of Copernicus depends upon the single question whether the ancient Greek was right or wrong when he said “ the heavenly bodies are infinitely distant.” It is a very insecure foundation for the whole of Copernican or modern astronomy to rest upon, but such indeed is the case.
Some thirty years after the publication of the work of Copernicus, Tycho Brahe, the Danish astronomer, invented the first instrument used in modern astronomy.
This was a huge quadrant nineteen feet in height (the forerunner of the sextant), which he used to very good purpose in charting out the positions of many of the more conspicuous stars. He differed with some of the details of the Prussian doctor’s theory, but accepted it in the main ; and took no account whatever of the question of the distance of the stars.
Immediately following him came Johann Kepler, and it is a very remarkable circumstance that this German philosopher, mystic and astrologer, should have been the founder of what is now known as Physical Astronomy. Believer as he was in the ancient doctrine that men’s lives are pre-destined and mysteriously influenced by the stars and planets, he nevertheless sought to discover some physical law which governed the heavenly bodies. Having accepted the Copernican Theory that the sun was the centre of the universe, and that the earth and the planets revolved around it, it was but natural that all his reasonings and deductions should conform to those ideas, and so it is only to be expected that his conclusions dealing with the relative distances, movements and masses of the planets, which he laboured upon for many years, and which are now the famous “Laws of Kepler,” should be in perfect accord with the Heliocentric Theory of Copernicus.
But, though the underlying principles of Kepler’s work will always have great value, his conclusions cannot be held to justify Copernican astronomy, since they are a sequel to it, but— on the contrary— they will be involved in the downfall of the theory that gave them birth.
While the life work of Johann Kepler was drawing to a close, that of Galileo was just beginning, and Ms name is more widely known in connection with modern astronomy than is that of its real inventor, Nicholas Copernicus. Galileo adopted the Copernican theory with enthusiasm, and propagated it so vigorously that at one time he was in great danger of being burnt at the stake for heresy. In the year 1642 he invented the telescope, and so may be said to have founded the modern method of observing the heavens.
Zealous follower of Copernicus as he was, Galileo did much to make his theory widely known and commonly believed, and we may be sure that it was because he saw no error in it that other giants of astronomy who came after him accepted it the more readily. Nearly eighteen hundred years had passed since Hipparchus had said the heavenly bodies were infinitely distant, and still no one had questioned the accuracy of that statement, nor made any attempt whatever to measure their distance.
It is interesting to mention here an event which— at first sight— might seem important, but which— now reviewed in its proper place in history— can be seen to have had a marked effect on the progress of astronomy as well as navigation. This was the publication of a little book called ” The Seaman’s Practice,” by Richard Norwood, in the year 1637.
At that time books of any kind were rare, and this was the first book ever written on the subject of measuring by triangulation. It was intended for the use of mariners, but there is no doubt that ‘ ‘ The Seaman’s Practice ” helped King Charles II to hearse how the science of astronomy could be made to render valuable service to British seamen in their voyages of discovery, with the result that in 1675 he appointed John Flamsteed to make a special study of the stars, and to chart them after the manner of Tycho Brahe and Galileo, in order that navigators might guide their ships by the constellations over the trackless oceans.
That was how the British School of Astronomy came into existence, with John Flamsteed as the first Astronomer Royal, employing only one assistant, with whom he shared a magnificent salary of £70 a year ; and navigation owes much to the excellent work he did with an old-fashioned telescope, mounted in a little wooden shed on Greenwich Hill.
At about the same time the French School of Astronomy came into being, and the end of the seventeenth century began the most glorious period in the history of the science, when astronomers in England, France and Germany all contested strenuously for supremacy, and worshipped at the shrine of Copernicus.