Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

September 14, 1996
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Aristarchus' Unbelievable Discoveries
Credit: Space Shuttle Columbia, STS58, NASA

Explanation: Here lived one of the greatest thinkers in human history. Aristarchus lived on the Greek island of Samos, a small island in the center of the above picture that can be identified with a good map. Aristarchus, who lived from 310 BC to 230 BC, postulated that the planets orbited the Sun - not the Earth -- over a thousand years before Copernicus and Galileo made similar arguments. Aristarchus used clear logic to estimate the size of the Earth, the size and distance to our Moon, the size and distance to our Sun, the the even deduced that the points of light we see at night are not dots painted on some celestial sphere but stars like our Sun at enormous distances. Aristarchus' discoveries remained truly unbelievable to the people of his time but stand today as pillars of deductive reasoning.

Tomorrow's picture: Tycho Brahe Measures the Sky

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA).
NASA Technical Rep.: Sherri Calvo. Specific rights apply.
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