earthshine

The faint illumination of the dark side of the Moon by sunlight reflected off the Earth — visible as a ghostly glow filling the unlit portion of a crescent moon. Leonardo da Vinci was the first to correctly explain it: the dark part of the Moon is lit by the bright Earth, just as a full moon lights the Earth at night. Earthshine varies with Earth's cloud cover — more clouds, more light reflected, brighter earthshine. It is our planet's light, returning to us from the Moon's surface.