Here's how it works:

* The Earth's Shadow: When the Earth passes directly between the Sun and the Moon, the Earth's shadow falls upon the Moon.

* Blocking Light: The Earth blocks the Sun's light from reaching the Moon.

* Types of Lunar Eclipses: There are three types:

* Total Lunar Eclipse: The entire Moon passes through the Earth's umbra (the darkest part of the shadow).

* Partial Lunar Eclipse: Only part of the Moon passes through the umbra.

* Penumbral Lunar Eclipse: The Moon passes through the Earth's penumbra (the lighter outer part of the shadow), causing a slight dimming of the Moon's surface.

Lunar eclipses are relatively common, but they don't occur every month because the Moon's orbit is tilted slightly.