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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesThe Moon’s shape does not change: sunlight always illuminates about half of it, and as the Moon orbits Earth we see different portions of that sunlit half. That changing view creates the familiar sequence of eight phases, from new Moon to full Moon and back again, over about 29.5 days.
Why the Moon changes shape
The Moon does not make its own visible light; moonlight is reflected sunlight. At any ordinary moment, the Sun lights one half of the Moon. As the Moon travels around Earth, the angle between the Sun, Moon and us changes, so the fraction of its lit hemisphere visible from Earth changes too. The Moon is not physically changing shape.
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Earth’s shadow does not cause the monthly phases. It falls on the Moon only during a lunar eclipse. NASA explains this distinction in its Moon phases guide and Top Moon Questions.
The complete phase cycle—from one new Moon to the next—takes about 29.5 days, according to NASA and NASA JPL Education. This is the repeating cycle of appearances, not the Moon’s orbital period measured against distant stars.
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The eight Moon phases, in order
The bright-side directions below follow the conventional Northern Hemisphere view used by NASA. In the Southern Hemisphere, or when your viewing angle is rotated, the bright side may appear on the opposite side.
- New Moon: The side facing Earth is mostly dark, so the Moon is usually difficult to see. It appears in roughly the same direction as the Sun and rises and sets near it. The Moon’s orbit is tilted relative to Earth’s orbit around the Sun, so it usually passes above or below the Sun rather than directly in front of it; not every new Moon causes a solar eclipse.
- Waxing Crescent: A thin crescent is visible and grows from day to day. In NASA’s Northern Hemisphere view, the lit edge is on the right.
- First Quarter: The visible disk looks about half illuminated. “Quarter” means the Moon is about one-quarter of the way through its phase cycle; it does not mean only one-quarter of the visible disk is lit.
- Waxing Gibbous: More than half the visible disk is lit, and the illuminated portion continues to grow toward full Moon.
- Full Moon: The visible face appears nearly fully illuminated. The Moon is opposite the Sun in the sky, so it generally rises around sunset and sets around sunrise.
- Waning Gibbous: More than half the visible disk remains lit, but the illuminated portion is shrinking after full Moon.
- Third Quarter (Last Quarter): The Moon again looks about half illuminated, with the bright side opposite the first-quarter view in the conventional Northern Hemisphere diagram. It is about three-quarters of the way through the cycle.
- Waning Crescent: A thin, shrinking crescent remains before the cycle returns to new Moon.
How to read phase names
- Waxing means the visible illuminated portion is growing as the Moon moves toward full Moon; waning means it is shrinking after full Moon.
- A crescent is less than half of the visible disk; a gibbous Moon is more than half lit but not full.
- First quarter and third/last quarter both look half-lit. “Quarter” describes progress through the cycle, not the fraction of the disk that appears bright.
When each phase is usually visible
These are broad patterns, not exact predictions. Moonrise and moonset depend on the date and your location; use a local moonrise calendar for specific times. NASA’s general guide gives these approximate patterns:
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| Phase | Approximate rise and set pattern |
|---|---|
| New Moon | Rises and sets near the Sun; usually hard to see because the near side is dark. |
| Waxing Crescent | Rises in the morning after sunrise and sets at night after sunset. |
| First Quarter | Rises around midday and sets around midnight; often high in the evening sky. |
| Waxing Gibbous | Rises in the afternoon before sunset and sets in the early morning before sunrise. |
| Full Moon | Rises around sunset and sets around sunrise. |
| Waning Gibbous | Rises after sunset and sets in the morning after sunrise. |
| Third/Last Quarter | Rises around midnight and sets around midday. |
| Waning Crescent | Rises in the very early morning and sets in the afternoon. |
For the phase illustrations and NASA’s viewing guide, see NASA Science: Moon Phases.
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