The Moon shines by reflected light. Normally, the light we see is light that is reflected from the Sun. However, the Moon also reflects light from Earth, and Earth reflects light from the Moon back onto the Moon. Earth's light can thus be seen on the Moon's "dark" section, but it is most easily visible during thin crescent phases soon after a New Moon, when the portion lit from the Sun is small in comparison to the rest of the globe.
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