Next Full Moon Calculator

In short A full moon happens at an instant, not on a day. The moon reaches an elongation of exactly 180 degrees from the sun at one moment, and that moment is the same everywhere on earth — so which calendar DATE a full moon falls on depends entirely on your time zone. The same full moon can be Tuesday morning in London and Monday evening in Los Angeles, which is why moon calendars disagree with each other and why this tool asks for your UTC offset rather than guessing. The interval between one full moon and the next averages 29.530589 days but is not constant, ranging from about 29.28 to 29.82 days, because both orbits are ellipses and the geometry does not repeat at a fixed rate. That average is also where a blue moon comes from: a year is 365.24 days and a lunar cycle is 29.53, so 12.37 cycles fit in a year and roughly every two and a half years there is a thirteenth full moon to fit somewhere. A common question is why there is not an eclipse at every full moon. The answer is that the moon orbit is tilted about 5 degrees to the earth orbital plane, so at most full moons the moon passes above or below the earth shadow rather than through it. An eclipse needs a full moon that also happens near one of the two points where the orbits cross, which is why eclipses arrive in seasons a few times a year instead of monthly.