![]() ![]() Inability to observe it left astronomers with only two alternatives: either the stars were so remote that it was impossible to detect displacement, or the earth would have to remain at rest. Of course it was impossible to observe stellar displacement without the aid of a telescope. He, as we shall see, had a much better appreciation of the sun’s great distance than Copernicus. Hipparchus continued to make improvements in the next century. To appreciate these developments we need only recall the careful stellar catalogues of Aristyllus and Timocharis early in the third century B.C., the work of the latter enabling Hipparchus to discover the precession of the equinoxes, and the armillary sphere of Eratosthenes by which he was able to determine the obliquity of the ecliptic and the circumference of the earth. Now it so happened that Aristarchus reached his conclusions at the very time when interest was keen at Alexandria and elsewhere in the Greek world in accurate observations and when marked improvements were being made in precision instruments. The more accurate the astronomical instruments and the greater the estimated distance of the sun, the more reason should there be to expect stellar displacement. Over such vast distances some displacement in the positions of the stars ought to be observed. As soon as the earth is set in motion in an annual revolution about the sun, the distance between any two of the earth’s positions that are six months apart will be twice as great as the earth’s distance from the sun. There is one objection that immediately arises when the earth is put in motion, the very difficulty which must have disquieted Copernicus and which caused Tycho Brahe shortly afterwards to renounce Copernicus’ heliocentric system and to put the earth again at rest. (Tycho reverted to a system first suggested by some ancient Greek, who made the planets revolve about the sun and the sun about the earth.) The difficulty is this. Let us now suppose that Aristarchus’ theory was widely circulated and that it was given careful consideration by leading astronomers. Here was laid the foundation upon which modern astronomy was built. We are indebted to the Alexandrians and Hipparchus for turning away from speculation to take up the recording of precise astronomical data. In developing the heliocentric theory the Greeks had run the gamut of theorizing. This paper then examines possible reasons for the Greek abandonment of the heliocentric theory and concludes that there is no reason to deplore its abandonment. From The Greek Heliocentric Theory and its Abandonment: I dug a little bit deeper, and this seems to be more or less accurate. But they remain ever fixed in the same place in the Heavens, therefore the Earth must be still (geocentric). If the Earth actually did move around the Sun, then the stars would logically have to appear different from one time to another. Based on that, they rejected the heliocentric hypothesis. How? They measured parallax.(Difference in stellar appearance from spring to fall, when we’re on opposite sides of the Sun.) Given the insensitivity of their measurement tools at the time, the stars didn’t change positions at all when the Earth moved to the other side of the Sun. They reasoned to the geocentric conclusion based on quantitative evidence. According to Astronomer Lisa, it’s not true that the Greeks simply thought they and their Gods were at the centre of the Universe because they were egotistical. Especially don’t follow it up by saying that science marches toward the Truth whilst religion thwarts its progress. The Greeks had the right theory (heliocentric solar system) but discarded it on the basis of experimental evidence! Never preach to me about progress-in-science when all you’ve heard is a one-liner about Popper and the communal acceptance of general relativity. Now this is the kicker in your Popperian dirtsack. But it seems as if the real story is more complicated than that: I had always heard that the Greeks embraced a geocentric universe for common-sense, aesthetic reasons - not scientific ones. Summary: The Greeks likely rejected a heliocentric theory because it would conflict with the lack of any visible stellar parallax, not for egotistical, common-sense, or aesthetic reasons. ![]()
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