Moon phase today – lunar calendar, next full moon and new moon

Is it a full moon tonight, how many days until the next new moon, and which way round does a waxing crescent look from Sydney? The phase of the moon is one of the few things in the sky that is the same for everyone at the same moment: the sun lights half of the moon, and as the moon goes around the earth we see more or less of that lit half. This page answers the question at once from your device's clock, before you click anything. The big picture shows the moon as it is now, the panel names the phase and gives the share of the disc that is lit and the number of days since the last new moon, and the next four principal phases are listed with their date, time and a countdown. Below it, a calendar draws the moon for every day of the month, and a table lists every full moon and new moon of the year with supermoons and blue moons marked. Pick any date to see its phase, step through the months, and choose whether the moon is drawn as seen from the north, the south or near the equator, where a crescent lies on its back. Choose a town or click the map and the times switch to that place's time zone, with moonrise and moonset added.

How to use it

1. Open the page; the phase for this moment appears at once, with times in your device's time zone.
2. Choose "Seen from" to draw the moon as it looks from the northern hemisphere, the southern hemisphere or near the equator.
3. Pick a date, or use −1 month and +1 month in the calendar, to see the phase on any day; click a day to show it.
4. Search a town or click the map to get its time zone, moonrise and moonset, then download the year as CSV or copy the share link.

How accurate is it?

How the phase is calculated

The phase comes from the angle between the moon and the sun seen from the earth. The moon's position is computed with chapter 47 of Jean Meeus' Astronomical Algorithms, a shortened ELP-2000/82 theory, and the sun's with chapter 25. New moon, first quarter, full moon and last quarter are the instants when the moon's longitude is 0°, 90°, 180° and 270° ahead of the sun's; the tool finds each to the second. Against the PyEphem ephemeris the instants agree within two minutes and the lit share within 0.3 percentage points.

Why the time zone matters more than the place

Everyone on earth sees the same phase at the same instant; parallax changes the lit share by less than a tenth of a percentage point between two places. What changes is the clock. A full moon at 23:30 in London is at 00:30 the next day in Paris, so printed calendars from two countries can put it on different dates. Until you choose a place, the page uses your device's time zone; afterwards, the place's own, with its summer time rules from the IANA time zone database.

What a day in the calendar shows

Each day in the calendar is drawn with the lit share at local midday. A day that holds a principal phase shows the time of that phase instead of the percentage, and each phase is shown on exactly one day. The phase name for a moment follows the angle to the sun: within 6° of an exact phase, about half a day either side, the moon is called new, first quarter, full or last quarter; between them it is a crescent or gibbous.

Good to know

Waxing on the right, but only in the north

In Europe and North America a waxing moon is lit on the right and a waning moon on the left, which gives the old rhyme that a moon shaped like a D is growing. South of the equator it is the other way round, and in the tropics the lit side of a crescent points down towards the sun below the horizon, so the moon looks like a bowl or a boat. The "Seen from" choice redraws the big moon and the calendar for each case; it is guessed from your time zone until you choose. With a place chosen, the big moon is drawn tilted as it really stands in that sky at the chosen time.

A lunar month is not 28 days

From one new moon to the next takes 29.53 days on average, the synodic month, but single months vary from about 29.3 to 29.8 days because the moon's orbit is an ellipse and the earth's speed around the sun changes. The moon's age in days therefore says how long ago the last new moon was, not exactly how far through the cycle the moon is. Twelve lunar months make 354 days, so the full moons move about 11 days earlier each year, and some years have 13 of them.

Full is a moment, and the eye cannot tell

The moon is exactly full only at one instant, but for about a day either side more than 97 % of the disc is lit, and no one can see the difference. That is why the moon looks full on two or three nights in a row. The share lit changes slowly around full and new moon and fastest around the quarters, by about 12 percentage points a day.