The eight names describe one continuous cycle
| Phase | What the name means | A useful viewing window |
|---|---|---|
| New Moon | Sunlit side mostly faces away from Earth | Usually lost in the Sun’s direction |
| Waxing crescent | Lit portion increasing, less than half | Early evening |
| First quarter | About half the visible disk lit | Afternoon and evening |
| Waxing gibbous | Increasing, more than half | Afternoon into the night |
| Full Moon | Visible face almost fully lit | Approximately sunset to sunrise |
| Waning gibbous | Lit portion decreasing, more than half | Later night and morning |
| Last quarter | About half the visible disk lit | Late night and morning |
| Waning crescent | Decreasing, less than half | Before sunrise |
These are broad windows, not rise-and-set predictions. Your latitude, the date and the local horizon change the details. The cycle from one new Moon to the next takes about 29.5 days.
Why phases are not Earth’s shadow
A normal crescent is the Moon’s own night side turned partly toward us. Earth’s shadow is involved in a lunar eclipse, which is a different event. An eclipse does not happen at every full Moon because the Moon’s orbit is tilted relative to Earth’s path around the Sun.
A first-quarter Moon looks half lit because “quarter” counts the fraction of the cycle completed since new Moon, not the fraction of the disk illuminated.
Waxing means the illuminated fraction is growing; waning means it is shrinking. Do not rely on “right side bright” as a worldwide rule. The Moon’s orientation changes with your hemisphere and its angle in the sky.
A full Moon is bright; a partial Moon is full of shadows
For binoculars or a small telescope, look near the terminator: the boundary between lunar day and night. Low-angle sunlight casts shadows across crater walls and mountains, making their shapes easier to read.
Near full Moon, the light reaches the middle of the disk more directly. Many shadows shorten and the landscape can look flatter. Full Moon has other rewards, including the bright rays around some impact craters.
Use a steady view and moderate magnification. Never scan near the Sun to find a thin crescent. You can learn plenty from an easy evening quarter Moon without attempting a difficult near-Sun observation.
Why the Moon is sometimes out in daylight
The Moon spends much of its orbit away from the Sun’s exact direction. When it is above your horizon and bright enough against the blue sky, you can see it during the day. An afternoon first-quarter Moon is an especially approachable example.
The Moon keeps nearly the same face toward Earth because its rotation and orbit are synchronized. That does not mean the far side is always dark. Both near and far sides receive sunlight over the month.
Give yourself a three-evening project
Find a waxing Moon on three clear evenings at roughly the same time. Notice its changing shape and position relative to the stars. A quick sketch is enough; compare the observations afterwards.
If your aim is to see faint galaxies or the Milky Way instead, check when the Moon is below the horizon. “It is not full” is not the same as “the sky will be dark.” A bright gibbous Moon can wash out faint structure for much of the night.
Sources and image credits
- NASA: top Moon questions. Phases, eclipses, daytime visibility and the far side.
- NASA: moonlight. Reflected sunlight and changing illumination.
- NASA: finding good places to stargaze. Moonlight and faint-object observing.
Written for beginners from the sources above. How we research and correct the library. Found an error? Tell us.