When Is the Next Full Moon?

How long does a full moon last?

Strictly, only an instant: the moment the moon is exactly opposite the sun in its orbit, which is the time given in the tables above. To the eye, though, the moon looks full for about three nights, because it is more than 97% lit for about a day and a half on either side of that moment. That's why the night before or after is just as good for watching, and why calendars sometimes list the full moon on the day before or after the one shown here: the exact moment falls on different dates in different time zones.

Why the full moon is so bright, and why it looks huge when it rises

At full moon, the side facing us is lit head-on, with no shadows from mountains or craters to darken it, so it is much brighter than at first or last quarter.^[7] Its distance changes over the year too: a full moon at the closest point of the moon's oval orbit, a supermoon, can look up to 14% bigger and 30% brighter than the year's smallest full moon.^[14] The huge moon you sometimes see sitting on the horizon is a different thing: an illusion of the eye. Measured, the rising moon is no bigger than when it is high in the sky.

Why the full moon rides high in winter and low in summer

A full moon sits opposite the sun, so it takes the path the sun takes six months later. In winter, when the sun is low, the full moon climbs high and stays up for most of the long night; in summer it stays low. In New York the December full moon can reach about 73° above the southern horizon, while the June full moon gets only to about 26°. In the Southern Hemisphere it's the other way round, with the high full moons in June and July.

Full moon names

The monthly names, from the Wolf Moon in January to the Cold Moon in December, come from North American traditions collected by The Old Farmer's Almanac.^[17] The full moon nearest the September equinox is the Harvest Moon and the next one the Hunter's Moon; a second full moon in one calendar month is a Blue Moon. Because the names follow the seasons of the Northern Hemisphere, they don't fit Australia or New Zealand, where the Harvest Moon would come in March or April. A Blue Moon also depends on your time zone: a full moon right at the end of a month can be the second of that month in one place and the first of the next in another.

Full moon and Purnima

In the Hindu calendar the full moon day is Purnima, the fifteenth tithi of the bright fortnight.^[51] Because festival days follow the tithi at sunrise, Purnima can fall on the day before or the day of the exact full moon in India. Our Moon Phase Today page shows the exact start and end of the next Purnima tithi for your city.

How we calculate

Every full moon is the moment the moon reaches 180° from the sun in longitude, calculated from the positions of the sun and moon; the cycle averages 29.53 days.^[6] Times are shown in the time zone of the place you choose. We count a full moon as a supermoon when it is closer than 362,500 km; there is no official definition, so other sites draw the line a little differently. City data come from GeoNames.^[37]