Moon phase today

Why the Moon has phases

The Moon makes no light of its own. As NASA explains, the Sun always lights one half of it, and the other half is in darkness. The Moon orbits Earth, and as it moves, we see that sunlit half from a changing angle. Between Earth and the Sun, its lit side faces away from us (new moon). On the far side of Earth from the Sun, we see the lit side face-on (full moon). Every phase between is a different mix of the lit and dark halves.

One full cycle, from new moon to new moon, takes about 29.5 days. This is the synodic month. The Moon completes an orbit relative to the stars in about 27.3 days, but needs about two more days to catch up with the Sun’s changing direction as Earth moves along its own orbit.

The eight phase names

Four phases are exact moments: new moon, first quarter, full moon and last (third) quarter. The stretches in between have their own names, giving eight in all:

1. New moon: the Moon is near the Sun in the sky and is not visible.
2. Waxing crescent: a thin sliver in the western sky after sunset.
3. First quarter: half of the disk lit, on the right side as seen from the US.
4. Waxing gibbous: more than half lit, and growing.
5. Full moon: the whole disk lit, opposite the Sun.
6. Waning gibbous: more than half lit, and shrinking.
7. Last quarter: half lit, now on the left side.
8. Waning crescent: a thin sliver in the east before dawn.

Waxing means the lit part is growing, from new moon to full. Waning means it is shrinking, from full back to new. “Quarter” means a quarter of the way through the cycle, even though half the disk is lit. Our guide to moon phases explained goes into more detail.

Why the Moon rises about 50 minutes later each day

Earth turns once a day, but the Moon moves eastward along its orbit at the same time, covering about one-thirtieth of the sky each day. After one day, Earth has to rotate a little further to bring the Moon back above the horizon. NASA puts the average delay at about 50 minutes a day.

That delay is why each phase belongs to a time of day. A full moon rises around sunset and is up all night. A first-quarter moon rises around midday and is high at dusk. A last-quarter moon rises around midnight and is still up in the morning sky. A new moon rises and sets with the Sun.

The 50 minutes is an average. In early autumn the delay shrinks enough to create the Harvest Moon effect.

Libration: seeing a little more than half

The Moon spins once per orbit, so it keeps the same face toward Earth. That face is not perfectly fixed, though. The Moon’s speed along its elliptical orbit changes, and its orbit is tilted, so over the month it seems to rock slightly from side to side and nod up and down. This is called libration. NASA’s Scientific Visualization Studio says libration lets us see about 59% of the Moon’s surface over time, not just 50%.

For the names and dates of each month’s full moon, see our full moon names pages.