What is a Lunar Eclipse?

The Earth casts a long shadow into space, and when this shadow passes over the Moon, it causes an eclipse.

A lunar eclipse can only happen during a full moon, when the Sun is directly behind the Earth. As the Moon travels around the Earth, it can move out of the Sun's light and into the shadow cast by Earth. But the Moon's path does not take it through Earth's shadow on each orbit. So the moon is not eclipsed every time it travels around the Earth, only up to three times each year. When the moon is completely in Earth's shadow, it is a total lunar eclipse. When the Moon is only partially covered by shadow it is a partial lunar eclipse.

Lunar eclipse can last for over one hour, but they do not completely black out the shadowed part of the Moon. Some sunlight always filters through, making the shadow look a reddish-brown color.