A total solar eclipse occurs when the Moon passes directly between Earth and the Sun.

The longer version

Solar eclipses require a rare alignment, because the Moon's shadow cone is narrow and only sweeps a small track across Earth's surface. The Sun and Moon happen to appear almost the same size in our sky, which allows the Moon to cover the disk almost exactly. The orbit is tilted, so alignments do not happen every month.

Totality lasts only a few minutes at any one place, and the shadow races across the globe. During those moments the sky darkens, temperatures drop and the faint outer atmosphere becomes visible. Partial eclipses are seen over a much wider area, and annular eclipses occur when the Moon sits farther away.

Where this entry sits

The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.