What is a lunar eclipse?

A lunar eclipse happens at a full moon when the Sun, Earth, and Moon line up so that Earth shadow falls across the Moon. Unlike a solar eclipse, it is safe to watch with the naked eye and can be seen by everyone on the night side of Earth at once. During a total lunar eclipse the Moon does not go completely dark; instead it often glows a deep red, because sunlight bending through Earth atmosphere is filtered so that mostly red light reaches the Moon. This dramatic colour has earned the event the nickname blood moon. Lunar eclipses do not happen every month because the Moon orbit is slightly tilted relative to Earth orbit around the Sun.