Bruce Murray Space Image Library

Copernicus and Eratosthenes

Copernicus and Eratosthenes
Copernicus and Eratosthenes These two craters -- Copernicus, left, and Eratosthenes, right -- give their names to two of the Moon's geologic periods. The Copernican period is the most recent one; Copernican-age craters have visible rays. The Eratosthenian period is older than the Copernican; its craters do not have visible rays. NASA / GSFC / ASU

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