Aristarchus

Aristarchus (310 BC - circa 230 BC) was a Greek astronomer and mathematician, born in Samos, Greece. He is the first recorded person to propose a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the "Greek Copernicus"). His astronomical ideas were not well-received and were subordinated to those of Aristotle and Ptolemy, until they were successfully revived and developed by Copernicus nearly 2000 years later.

Size of the Moon

Aristarchus observed the Moon moving through the Earth's shadow during a lunar eclipse. He estimated that the diameter of the Earth was 3 times the Moon's diameter. Using Eratosthenes' calculation that the Earth was 42,000 km in circumference, he concluded that the Moon was 14,000 km in circumference. The Moon has a circumference of about 10,916 km.

Related Topics:
Moon - Lunar eclipse - Eratosthenes - Circumference

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