Earthlight (astronomy)

Earthlight is the light that comes from the Earth and shines on the Moon. The Moon doesn't have any light of its own, so it's mostly dark. However, when the Sun shines on the Earth, some of that light bounces off and reflects onto the Moon. This light is called earthlight, and it lights up the parts of the Moon that aren't facing the Sun.

You can see earthlight when the Moon is in a certain phase, like when it's a crescent or a quarter Moon. During these phases, the part of the Moon that is facing the Earth is only getting a little bit of sunlight. But because the Earth is so much bigger than the Moon, the part of the Earth that is facing the Moon is getting a lot of sunlight. Some of this sunlight gets reflected onto the part of the Moon that's not facing the Sun, and that's what we call earthlight.

Earthlight is a really cool thing to see, especially if you have a telescope or binoculars. When you look at the Moon during a crescent or quarter phase, you can see the dark part of the Moon lit up by this faint glow. Some people even say that they can see the Earth's continents and oceans reflected in the earthlight on the Moon, although that's a little hard to believe!