The Moon's phases come from changing angles between the Moon, Earth, and the Sun.

The longer version

Lunar phases depend on geometry alone. Half the Moon is always lit by the Sun, but the fraction of that lit half facing Earth changes as the Moon moves along its orbit. No shadow of Earth is involved in the ordinary monthly cycle. The cycle repeats roughly once a month.

When the Moon sits between Earth and the Sun we see the unlit side, and when it lies on the far side we see a full disk. Between those extremes come crescents and gibbous shapes. The same hemisphere always faces us, so the pattern of dark plains looks fixed.

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.