Moon phases: today's moon

How it works

Phase dates and times are computed with Jean Meeus' astronomical algorithms (the same used by almanacs), accurate to the minute. Times are shown in your device's time zone.

Waxing or waning?

In the northern hemisphere: if the lit side is on the right, the Moon is waxing; if it's on the left, it's waning.

Twenty-nine and a half days, not twenty-eight

A full cycle of phases lasts 29 days, 12 hours and 44 minutes on average, not twenty-eight as people often say. It is the synodic month, the time the Moon takes to return to the same position relative to the Sun as seen from Earth.

The number 28 comes from the sidereal month (27.3 days), the time for one full circuit relative to the stars. The two differ because in the meantime the Earth has moved along its own orbit, and the Moon has to make up that stretch to line up with the Sun again.

Telling waxing from waning by eye

In the northern hemisphere the rule is the lit side facing west: if the bright part is on the right (towards the west, where the Sun sets) the Moon is waxing; if it is on the left it is waning. A «D» shape is waxing, a «C» shape is waning.

The rule flips in the southern hemisphere, where the same Moon is seen upside down, and near the equator the crescent appears horizontal, like a little boat. It is why the sayings learned at school stop working once you go below the tropics.

Supermoon, blue moon and other labels

A supermoon is a full moon falling near perigee, the point of the orbit closest to Earth: it looks about 7% larger and 15% brighter than usual. The difference is real but hard to see by eye, with nothing beside it for comparison.

A blue moon is not blue: it is the second full moon in the same calendar month, a fact about calendars and not about astronomy. And the illusion that makes the Moon look huge on the horizon is exactly that, an illusion: photographed, it is the same size as when it is high in the sky.

Nearby tools

For daylight there is Sunrise and sunset, and for the equinoxes Start of the seasons. If you need the weekday of a past date, look at What day was it.