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The Question

(Submitted February 12, 1998)

I am interested in finding out who was the first to discover that the earth and the rest of the planets revolve around the sun.

The Answer

The Greek astronomer Aristarchus, who lived in the first half of the third century BC, is credited as being the earliest known person to suggest that the earth revolves around the sun. Aristotle, who lived in the 4th century BC, had considered such an idea. But he rejected that idea because he thought that the motion of the earth around the Sun would cause a regular shifting in the positions of the stars. This shifting is called parallax, and Aristotle didn't see this occur. However, Aristotle was unaware of the enormous distances to the stars, which make such motion unobservable without telescopes.

In the modern era, Nicholas Copernicus is credited as setting the heliocentric model of the solar system on a firm footing. He wrote about this in 1543. In 1609 Johannes Kepler used the very accurate observations of Mars made by Tycho Brahe (in the 1590's) to demonstrate that the position of Mars could be accurately predicted using sun-centered solar system suggested by Copernicus.

Jim Lochner
for Ask an Astrophysicist

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