During the total lunar eclipse, the moon is not totally dark

The Moon does not completely disappear because of the refraction of sunlight by the Earth's atmosphere into the shadow cone. The red colouring arises because sunlight reaching the Moon must pass through a long and dense layer of the Earth's atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the small particles, and so by the time the light has passed through the atmosphere, the longer wavelengths of red light dominate.

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