An eclipse occurs when the normal sunlight received by the Earth or the Moon is blocked because the paths of the Moon and Earth cross. Sometimes the Earth blocks out light reaching the Moon, giving an eclipse of the Moon; more spectacularly, the Moon blocks out light reaching the Earth, giving an eclipse of the Sun.

The most spectacular eclipse we see on Earth is the eclipse of the Sun. Although the Moon is much smaller than the Sun, it is much nearer to the Earth and appears as large as the Sun in the sky. When the Moon eclipses the Sun, it covers it completely, and places on the Earth that are in its shadow see the sky go as dark as night.

Sometimes only part of the Moon covers the Sun. This is called a partial eclipse.