The eight moon phases
One full cycle, new moon to new moon, takes about 29.5 days. Here is each phase in order, what it looks like, and what it is taken to mean.
1. New Moon
A new moon is the moment the moon sits between Earth and the sun, so the half we can see is entirely unlit and the moon is invisible from the ground.
What it means →2. Waxing Crescent
A waxing crescent is a moon less than half lit and growing, with the lit sliver on the right side of the disc as seen from the Northern Hemisphere.
What it means →3. First Quarter
A first quarter moon is exactly half lit and growing, with the right half of the disc bright, and it marks one quarter of the way through the lunar cycle.
What it means →4. Waxing Gibbous
A waxing gibbous is a moon more than half lit and still growing toward full, with the bulge of light on the right side of the disc in the Northern Hemisphere.
What it means →5. Full Moon
A full moon is the moment the whole visible face is lit, when the moon sits opposite the sun with Earth between them.
What it means →6. Waning Gibbous
A waning gibbous is a moon more than half lit and shrinking after full, with the light now on the left side of the disc in the Northern Hemisphere.
What it means →7. Last Quarter
A last quarter moon is exactly half lit and shrinking, with the left half of the disc bright, three quarters of the way through the lunar cycle.
What it means →8. Waning Crescent
A waning crescent is a moon less than half lit and still shrinking toward new, with the thin sliver of light on the left side of the disc in the Northern Hemisphere.
What it means →How to read the shape
Two questions tell you everything. How much is lit? Less than half is a crescent, exactly half is a quarter, more than half is gibbous, all of it is full, none of it is new. Which side is lit? In the Northern Hemisphere, light on the right means waxing and growing, light on the left means waning and shrinking. South of the equator both are mirrored.
Put those together and any moon in the sky names itself. A fat moon lit on the left is a waning gibbous, roughly five days past full. There is a fuller walkthrough in how to read moon phases.
Why the cycle is 29.5 days and not 27
The moon completes one orbit of Earth in 27.3 days, but in that time Earth has moved along its own orbit around the sun, so the moon needs about two more days to catch up to the same alignment with the sun. The phase cycle you see, the synodic month, is that longer figure: 29.53 days.
Common questions
What are the eight moon phases in order?
New moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent. The cycle then repeats, taking about 29.5 days from one new moon to the next.
What does my moon phase mean?
Your moon phase is the shape the moon was in on a date that matters to you, usually your birthday. It is described by how much of the disc was lit and whether that light was growing or shrinking. Enter a date on this page to find yours, then read what that phase is traditionally taken to mean.
How do you tell a waxing moon from a waning one?
Look at which side is lit. In the Northern Hemisphere a moon lit on the right is waxing, growing toward full, and a moon lit on the left is waning, shrinking toward new. South of the equator it is the other way around.
What is the difference between a quarter moon and a half moon?
They are the same sight with two different names. Half describes the face you see, which is exactly half lit. Quarter describes the orbit, which is one or three quarters complete. Astronomers use quarter, so first quarter and last quarter are the standard terms.
What does gibbous mean?
Gibbous comes from the Latin for humped, and describes any moon more than half lit but not yet full. It is waxing gibbous on the way up to a full moon and waning gibbous on the way back down.
Next: see tonight's moon phase, find the moon on your birthday, or check whether two birthdays make a full moon.