The Earth in Greek Astronomy
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The Earth in Greek Science


November 2016 - Early Greeks thought of the Earth as the goddess Gaia, the mother of everything. Like a mother, the Earth gave food to people. By the time of Homer's Odyssey, Greek sailors knew the outline of the Mediterranean and the Black Sea quite well, and they knew something about the Red Sea, the Persian Gulf, and the Arabian Peninsula.

But by the Classical period, while some people still believed the earth was flat, educated Greeks like Thales knew that the earth was a round ball. Herodotus, in the 400s BC, knew that some people thought the ocean went all the way around Eurasia and Africa, though he wasn't sure this was right. Herodotus had heard stories that some people had sailed all the way around Africa, too. He knows that it's very cold in the north, too, and snows a lot. He knew the rivers of Eastern Europe and Ukraine: the Danube, the Dniester, the Bug, the Dnieper, the Inhul, the Molochna, and the Don, and further east: the Tigris and Euphrates, the Oxus, the Jaxartes, and the Indus.

By the Hellenistic period, about 200 BC, Greek-speaking scientists working in Egypt like Eratosthenes were able to use astronomy and geometry to measure the circumference of the earth (the distance around it).

Aristarchus, about 300 BC, used his observations of the eclipse of the moon to prove that the earth went around the sun instead of the sun going around the earth. Aristarchus also calculated that the sun must be much bigger than the earth and the moon, and that the stars must be very, very far away. Most other astronomers were skeptical of Aristarchus' ideas, even though they all turned out to be right. To the Greeks, who always placed man at the center of everything, it was hard to change that idea.

Learn by doing: observe a lunar eclipse
Greek ideas about the Moon

Bibliography and further reading about Greek astronomy and the Earth:

The Librarian Who Measured the Earth, by Kathryn Lasky (1994). An account of the life and work of Eratosthenes, who figured out the circumference of the earth. Explains how he did it. Easy reading.

Greek Astronomy, by Thomas Heath (1932). A collection of what ancient Greek writers had to say about astronomy, in their own words, with a long introduction. For adults.

The History & Practice of Ancient Astronomy, by James Evans (1998). Includes both the history, and directions to actually re-do the experiments that ancient Greek astronomers used to figure out their conclusions. For adults.

Greek Science After Aristotle, by G. E. R. Lloyd (1975).

More about Roman astronomy (Ptolemy)
More about Islamic astronomy home

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Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter, or buy her book, Vandals to Visigoths.
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  • Carr, K.E. . Study Guides, . Web. 28 March, 2017