Classical Greek Astronomy

Modern astronomy had its beginnings in a series of remarkable contributions by Greek astronomers in the classical Hellenic and early Roman periods. The rapid development of Greek science in the fourth century B.C. has been attributed to developments in writing, an expanding Greek empire, a new inquiring attitude, and the establishment of institutions of learning. Presumably the development of geometry (Euclid dates from about 300 B.C.), and the belief that nature might follow simple mathematical laws, were also crucial in stimulating this foundation period of astronomical research.

The Earliest Works

The earliest important contributions were made by Plato (428-348 B.C.) and Eudoxus (mid-4th century B.C.), who inquired into the motion of the planets using a geometrical model of the solar system. They assumed a spherical Earth (a complete departure from the flat Earth of creation myths) and a surrounding celestial sphere with fixed stars and the Sun, Moon, and planets moving on its surface. This initiated a series of astronomical works, some of which anticipated modern era results by two thousand years.

The Scientific Method
The application of mathematics to these models and careful comparisons with observation was a crucial development, because it made the different models testable through their predictions. This approach was due to Hipparchus (146-127 B.C.), and is essentially the modern scientific method.
The use of precise geometrical models led to impressive determinations of the circumference of the Earth by Erastosthenes (276-194 B.C.), which Columbus chose to ignore, and the distance to the Moon (Hipparchus).

Much of this work was simply a development of the early concentric spheres model; for example, Cyzicus and Aristotle (384-322 B.C.) increased the number of spheres in an attempt to explain differences in planetary motion (each planet was assigned one or more spheres). New models continued to appear however, and we find the suggestions that the Earth itself rotates with a twenty-four hour period (Heraclides, mid-4th century B.C.) and that the Sun, not the Earth, is at the center of the solar system (Aristarchus, 270 B.C.).

The Later Roman Period

Later works in the Roman period were largely compilations of previous Greek ideas, augmented with new observations of planetary motion and stellar positions. The best known of these is Claudius Ptolemy's Almagest (about A.D. 150, written in Greek-speaking Alexandria), which became the standard reference for astronomy in the Middle Ages. The figure below shows a portion of a Latin translation of Ptolemy's Almagest.