How does it work (what is a lunar eclipse)?
One face of the Earth always faces the Sun, and thus there is a “shadow” from the Earth that points outward into space on the opposite side from the Sun. The shadow lies in the Earth-Sun orbital plane. The moon has an orbit that is plane that tilts just slightly with respect to the Earth-Sun plane. Occasionally, the Moon will cross the Earth-Sun plane (twice an orbit) – and even more rarely, it will make that pass when the Earth’s shadow is there (causing the light from the Sun to be blocked by the Earth). [The Moon can also touch the Earth-Sun plane between the Earth and the Sun – causing a Solar Eclipse.] Notice that the adjective in front of the word eclipse tells what object is being “blocked” … a lunar eclipse has the Earth blocking the light to the Moon and a solar eclipse has the Moon blocking the light from the Sun.
