Astronomy is an area where the Greeks displayed a remarkable talent. Observational astronomy, which was the main form of astronomy elsewhere, was taken a step further in Greece: they attempted to build a model of the universe that could account for the observations. They explored all imaginable alternatives, they considered many different solutions for the various astronomical problems they came across. They not only anticipated many ideas of modern astronomy but also some of their ideas endured for around two millennia. Even at the time of Isaac Newton, some aspects of Aristotelian cosmology were still taught at the University of Cambridge.
Our knowledge of Greek astronomy before the 4th century BCE is very incomplete. We have just a few surviving writings, and most of what we know are references and comments form Aristotle, mostly opinions he is about to criticize. What is clear is that the earth was believed to be a sphere, and that there was an increasing effort to understand nature in purely natural term, without recourse to supernatural explanations.
The Greeks' neighbours, Egyptians and Babylonians, had highly developed astronomies, but the forces driving them were different. Egyptian administration relied on well-established calendars to anticipate the flooding of the Nile; rituals were required to be able to tell the time during the night, and the orientation of monuments in the cardinal directions was also important. Babylonians believed in the reading of omens in the sky as a mean to secure the state. These were all important stimuli to develop a fine astronomy.
Pythagoras is credited as the first Greek to think the earth spherical, but this idea was probably founded on mystic reasons rather than scientific. The Pythagoreans found conclusive evidence in favour of a spherical earth after it was discovered that the moon shines by reflecting light, and the right explanation for eclipses was found. The earth's shadow on the moon's surface suggested that the shape of our planet was spherical.
Aristotle's book "On the Heavens" summarizes some astronomical notions before his time. He says, for example, that Xenophanes of Colophon claimed the earth below us is infinite, that it has “pushed its roots to infinity”; others believed the earth rested upon water, a claim whose original author seems to be Thales (according to Aristotle); Anaximenes, Anaxagoras, and Democritus believed the earth was flat which “covers like a lid, the earth beneath it”.
Explanation:
https://www.worldhistory.org/Greek_Astronomy/
