The Phases of the Moon

Why does the Moon change shape?

The Moon is a spherical ball of rock. It does not produce its own light; it only reflects sunlight.

At any moment, exactly 50% of the Moon is lit by the Sun (the side facing the Sun), and 50% is in shadow. However, because the Moon revolves around the Earth, we see different amounts of that illuminated side.

The Cycle of Phases

The cycle from one New Moon to the next takes about 29.5 days.

1. New Moon: The Moon is between Earth and Sun. The lit side faces the Sun, the dark side faces us. We see nothing.
2. Waxing Crescent: A sliver of light appears on the right.
3. First Quarter: We see half of the Moon illuminated.
4. Waxing Gibbous: More than half is lit.
5. Full Moon: The Earth is between the Moon and Sun. We see the fully illuminated face.
6. Waning Gibbous: The light starts to shrink.
7. Last Quarter: We see the other half illuminated.
8. Waning Crescent: A sliver of light remains on the left.

Moonrise and Moonset

The Moon does not rise at the same time every day.

• Because the Moon moves in its orbit around Earth, it rises about 50 minutes later each day.
• New Moon: Rises at sunrise, sets at sunset (invisible).
• Full Moon: Rises at sunset, sets at sunrise (visible all night).
• Crescent Moon: Visible just after sunset (Waxing) or just before sunrise (Waning).