Moon phase
Astronomy Lunar phase
The Moon’s phase shows how much of its sunlit half we can see from Earth. It results from the positions of the Sun, Earth and Moon, not Earth’s shadow.
Half the sphere is illuminated
Except during a lunar eclipse, the Sun illuminates roughly half the Moon. As it orbits Earth, we see different portions of that half. A crescent grows to a half Moon, then a full Moon, before shrinking again.
The main phases
On small screens, scroll sideways to see all columns.
| Phase | What we see | Often visible |
|---|---|---|
| New Moon | The sunlit side faces mostly away from us. |
Near the Sun and usually invisible. |
| First quarter | About half the visible disc is lit. |
Afternoon and evening. |
| Full Moon | Almost the entire visible disc is lit. |
Mainly at night. |
| Last quarter | About half the disc is lit again. |
Late night and morning. |
“Quarter” describes the position in the phase cycle, so a half-lit quarter Moon is not an arithmetic mistake. New Moon to new Moon takes about 29.5 days on average.
Why full Moon is not best for everything
Bright moonlight makes faint galaxies and nebulae harder to see. For craters, long shadows near the boundary between light and dark often reveal more detail. Lunar altitude, rise and set times and angular distance from the target matter alongside phase.
The illuminated percentage describes only the bright fraction of the visible disc. The Moon’s brightness does not increase in the same proportion.