Illuminated by earthshine
Have a good look at the moon next time it is only a thin crescent. Only a sliver of sunlight is reflected off the moon towards the Earth however you will notice that you can see the “dark” part even though there is no direct sunlight falling on it. The reason it is visible is that it is illuminated by sunlight reflecting off the Earth, hitting the night side of the Moon, and bouncing back to the Earth.
The sunlight reflecting off the earth is referred to as earthshine.
The following image is a composite image of earthshine illuminating the moon during a solar eclipse.

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Filed under: astronomy

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