During an eclipse, the moon passes in front of the sun, with the alignment and size matching—while the Sun is about 400 times larger than the moon, it is also about 400 times farther away, meaning they appear the same size during an eclipse.

The moon is currently receding from Earth at a rate of between one and one-and-a-half inches per year. Eventually, when the moon moves far enough away, it will no longer be able to cover the sun in the way it does now.