Full moon dates
Full moon dates are the civil dates that contain the instant when the Moon is full. That instant is one moment; the local date can differ by time zone, and the list changes every year.
How it works
A full moon is an alignment, not a 24-hour festival. The Moon is full at a single instant, usually published in UTC. Your wall calendar then prints the local date that contains that instant. If the instant sits near midnight, one country can print Tuesday and another Wednesday for the same full moon.
The cycle from full moon to full moon is the synodic month, about 29.53 days. That is why the dates walk through the week and through the month instead of sticking to the 15th. A year usually holds twelve full moons. Some years hold thirteen, because twelve synodic months do not fill a civil year exactly.
The Moon can look round to the eye on the night before and the night after. That is appearance. The named full-moon date is the date of the instant, in the zone you are using. If you needed “the” date for a ritual or a tide table, use the instant and the zone, not a memory of last year’s Friday.
Why the date can flip
Take a full moon at 02:00 UTC. In London that is still the morning of that date. In a zone many hours west, it is still the previous evening. Both calendars are honest. They split a moment across a date line of clocks, not a disagreement about the sky.
May 2026 has two full-moon instants in UTC, on 1 May and on 31 May. Two full moons in one named month is the monthly sense of “blue moon.” That extra date is a civil-month accident: February is short, May is long, and 29.53 days can fit twice in a 31-day box. It is not a change in the Moon’s physics.
Full moon: one instant of alignment. Printed date: the local civil date of that instant. Spacing: about 29.53 days to the next full moon. Count in a year: twelve, sometimes thirteen. From Thursday 3 September 2026 the next full-moon instant is 26 September 2026 at 16:49 UTC, a Saturday in UTC. Zones far west of UTC can still be on Friday evening when that moment happens. Write the zone next to the date if the date has to survive travel.
Names, harvest moons, and lists that rot
Folk names — harvest moon, hunter’s moon — are labels on full moons in a season, not extra astronomical events. The harvest moon is the full moon closest to the September equinox. In 2026 that equinox is 23 September, and the 26 September full moon is the one sitting next to it. The name does not move the instant.
A list copied from last year is already wrong. The dates walk. A list without a time zone is incomplete. A list that treats the full moon as “all night on that date everywhere” is a poster, not a calculation.
Easter uses an ecclesiastical moon table, not this astronomical instant. Do not take a full-moon date from a sky almanac and assume it is Easter’s moon. Different tables, different jobs. The Moon is full in a moment. Your calendar only lends that moment a date, and it may lend a neighbour a different one.
Questions and answers
- When is the next full moon after 3 September 2026?
- 26 September 2026 at 16:49 UTC. Convert that instant to your local date.
- Why do two calendars disagree by a day?
- The instant is one. Midnight is local. Near midnight, the printed dates split.
- Are full moon dates the same every year?
- No. They walk by about 29.53 days and must be listed year by year.
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