Earthshine is the dark ash-grey light sometimes visible on the dark part of the crescent Moon. As the word suggests, it is caused by the bright light from Earth, being almost 100% illuminated as seen from the Moon, when the Moon appears for us as a crescent. Sometimes, when the Moon-facing side of Earth is largely covered by clouds, the Earthshine is so bright that one can see the lunar structures (craters and maria) in the dark part of the Moon even with the naked eye.
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