Earthshine reflecting off the moon. The bright region is directly illuminated by the sun, while the rest of the moon is illuminated by light reflected off the Earth.

Sometimes, when the moon is in one of its crescent phases, you might see a phenomenon known as earthshine, when the portions of the moon that are supposed to be in shadow glow faintly with a ghostly light.

This glow is actually light from the sun that has bounced off Earth to illuminate the dark side of the moon.

Astronaut John Young has said that the earthshine on the moon was quite bright enough for him to have landed his Apollo Lunar Module safely!