The moon's dark silhouette will glide across the face of the sun on September 1, giving most of equatorial Africa a rare view of an annular solar eclipse.

A solar eclipse occurs when Earth, the moon, and the sun line up so that the moon casts a shadow on our planet. However, not every eclipse looks the same. The moon follows an egg-shaped orbit around Earth, and the distance between the two objects varies over time. For sky-watchers, that means the apparent size of the lunar disk changes, too.

A total solar eclipse happens when the moon is close enough to Earth that it seems to completely cover up the sun. During an annular eclipse, though, the moon is farther from