The phases of the moon – moon calendar

The moon changes appearance in a fixed cycle of about 29.5 days, because we see different parts of its lit side as it moves around Earth. The moon calendar below shows the phase for every day of the month – use the arrows to browse back and forth.

The eight moon phases

• New moon 🌑 – the moon is invisible; read more about new moon.
• Waxing crescent 🌒 – a thin sliver of light grows.
• First quarter 🌓 – half the disc is lit and growing.
• Waxing gibbous 🌔 – more than half is lit.
• Full moon 🌕 – the whole disc is lit; read more about full moon.
• Waning gibbous 🌖 – the light begins to fade.
• Last quarter 🌗 – half is lit and waning.
• Waning crescent 🌘 – only a thin sliver of light remains.

Why does the moon change phase?

The moon does not shine by itself – it reflects sunlight. As the moon orbits Earth, the angle between the Sun, Earth and Moon constantly changes, so we see different parts of the lit half. This angle determines the phase and the illuminated fraction.

See also the moon today for your location, or the almanac with sun and moon together.

Why the moon looks different from north and south

A waxing crescent has its lit side to the right seen from the UK, but to the left seen from Australia. The Moon has not changed — the observer is simply upside down relative to the other one. Near the equator the crescent lies almost horizontally, like a bowl, which is the same phenomenon seen from halfway between the two.

It is also why the mnemonic that "a D is waxing and a C is waning" only holds in the northern hemisphere. In the south it is reversed.

The same side always faces us

The Moon takes just as long to rotate on its axis as it does to orbit the Earth — 27.3 days. That is why we always see essentially the same half. It is called tidal locking, and it is the result of tidal forces that slowed the Moon's rotation over billions of years until the two periods matched.

So the "far side of the moon" is not dark — it gets exactly as much sunlight as the near side. It is simply never visible from Earth. Small wobbles in the orbit, called libration, do let us glimpse about 59% of the lunar surface over time.

When each phase is in the sky

The phase of the moon and the time it is visible are the same fact stated two ways. The phase is determined by the angle between the moon and the sun as seen from Earth — and that angle also fixes when the moon rises and sets.

• New moon — rises at sunrise, sets at sunset. In the sky all day and invisible in the glare.
• First quarter — rises around midday, highest at sunset, sets around midnight. The classic early-evening moon.
• Full moon — rises at sunset, highest at midnight, sets at sunrise. Up for the whole night, and only the night.
• Last quarter — rises around midnight, highest at sunrise, sets around midday. The moon you see on the way to work.

Once this clicks, the sky becomes readable: a crescent low in the west after sunset must be a waxing moon a few days old, and a half moon high overhead at breakfast must be a last quarter. If you can see a lit moon in the afternoon, the lit edge points towards where the sun is.

Why there isn't an eclipse every month

If the moon passes between Earth and sun at every new moon, and Earth passes between sun and moon at every full moon, the obvious question is why we do not get a pair of eclipses monthly.

The answer is that the moon's orbit is tilted about 5° relative to the plane of Earth's orbit. Five degrees is small, but the sun and moon are each only about half a degree across, so most months the moon passes comfortably above or below the line and its shadow misses the Earth entirely — or the Earth's shadow misses it.

Alignments only work near the two points where the orbits intersect, called the nodes, and the Earth passes through that alignment roughly twice a year. That gives eclipse seasons rather than eclipse months: typically four to seven eclipses of one kind or another per year, clustered in two windows. See lunar eclipses for what happens when the alignment does come off.

We see more than half the moon

The moon is tidally locked, so the same face is always turned towards us — but "always" is not quite exact. Over a month the moon appears to rock very slightly, nodding north and south and rolling east and west, an effect called libration. It happens because the moon's orbit is elliptical, so its orbital speed varies while its rotation stays constant, and because its axis is tilted with respect to its orbit.

The result is that we can peek a little way around the eastern and western limbs at different times of the month, and over the shoulder of each pole. Cumulatively we can see about 59% of the lunar surface from Earth, not 50%. The remaining 41% was never seen by anyone until a Soviet probe photographed it in 1959 — and it turned out to look quite different, with far fewer of the dark basalt plains that give the near side its familiar markings.

The moon is not made of cheese, and other useful corrections

Two ideas about phases are worth actively dispelling. The first is that phases are caused by the Earth's shadow falling on the moon. They are not — phases are simply which part of the permanently lit half we happen to be looking at from our angle. The Earth's shadow on the moon is a lunar eclipse, which is a distinct and much rarer event.

The second is that there is a permanent "dark side" of the moon. There is a permanent far side, which we do not see from Earth, but it receives exactly as much sunlight as the near side does — just on the opposite schedule. At new moon, when the near side is completely unlit, the far side is in full daylight.

For today's phase and illuminated fraction at your own location, use the almanac or the moon today. For upcoming dates, see full moons and new moons.

Frequently asked questions about moon phases

How many moon phases are there?

There are eight named moon phases in a full cycle: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter and waning crescent.

How long is a lunar cycle?

A full cycle from new moon to new moon lasts about 29.5 days. This is called a synodic month.