Why does a lunar eclipse only last a few hours?

Answer 1

It lasts as long as a solar eclipse, but is seen around the globe simultaneously. In a solar eclipse, the Moon's shadow is visible at different times as it moves across the face of the Earth. The Earth, being larger, casts a shadow larger than the Moon.

But as the Moon is constantly moving around the Earth, it can only stay in Earth's shadow until it has moved about one planetary diameter, then it is no longer in the shadow. The distance is about 12,750 kilometers at a speed of about 1.022 km/sec -- this equals about 3.46 hours in partial or complete shadow. The eclipsed Moon turns dark red, rather than black, because the Earth's atmosphere scatters sunlight around the planet, mostly in the red frequencies.