Ancient Greek astronomy

Ancient Greek astronomy combined observations of celestial phenomena with geometrical models and theories about the structure of the cosmos, from the archaic period through late antiquity.

Geocentric model: A model that places Earth at or near the center of the cosmos, with celestial bodies moving around it. Greek astronomers developed mathematical systems that placed Earth at the center of celestial motion.
Eudoxus of Cnidus: A fourth-century BCE Greek mathematician and astronomer who modeled celestial motions with nested homocentric spheres. His sphere system was an early mathematical account of the planets' complex appearances.
Almagest: Ptolemy's second-century CE mathematical treatise presenting models and tables for the motions of the Sun, Moon, and planets. It systematized earlier Greek astronomy into a detailed predictive framework.
Aristarchus of Samos: A Greek astronomer of the third century BCE who proposed that Earth rotates and revolves around the Sun. His heliocentric proposal diverged from the geocentric framework that later dominated Greek astronomy.
Ptolemy: A second-century CE Greek-speaking scholar in Alexandria whose writings treated astronomy, geography, and optics. His synthesis became the principal reference for mathematical astronomy for many centuries.
Deferent and epicycle: A system representing a planet's motion with a small circle carried along a larger circle centered near Earth. This construction reproduced planetary loops within a broadly Earth-centered model.
Hipparchus: A Greek astronomer of the second century BCE known for precise observations, a star catalogue, and mathematical astronomy. His observations and methods set standards later used by Ptolemy.
On the Sizes and Distances (Aristarchus): A surviving work by Aristarchus of Samos estimating the relative distances and sizes of the Sun and Moon. Its geometric arguments illustrate how Greek astronomy inferred cosmic dimensions from observations.
Philolaus: A fifth-century BCE Greek philosopher who placed a central fire, rather than Earth, at the cosmos's center. His cosmology shows that alternatives to a stationary central Earth appeared before Aristarchus.
Theon of Alexandria: A fourth-century CE mathematician and commentator who edited and explained works including Ptolemy's Almagest. His commentaries helped preserve and transmit Greek astronomical texts in late antiquity.

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