Lunar Calendar & Moon Phases

About moon phases and the lunar calendar

The Moon shows phases because sunlight always lights half of the lunar globe, while the share of the lit half facing Earth changes as the Moon orbits. At new moon the Moon sits roughly between Earth and the Sun and the lit side faces away. At full moon the Moon sits on the far side of Earth and the whole lit half faces Earth. First quarter and last quarter fall halfway between, when exactly half of the visible disc is lit. The phases between those four moments are the waxing crescent, waxing gibbous, waning gibbous and waning crescent.

The synodic month

One full cycle from new moon to new moon takes about 29.53 days on average, a period called the synodic month or lunation. The Moon's elliptical orbit and the pull of the Sun stretch or shorten single lunations by up to about seven hours, so the gap between two full moons varies from roughly 29.3 to 29.8 days. Twelve lunations last about 354 days, eleven days short of a calendar year, which is why the phase dates shift earlier each year.

Why dates differ by time zone

Each phase is a single instant, the same everywhere on Earth. A full moon at 02:00 UTC on 3 January falls on the evening of 2 January in New York and on the morning of 3 January in Tokyo. The table shows times in the time zone of this browser or in UTC, and the Blue Moon marking and day numbers follow the chosen zone.

Blue Moon and supermoon

A Blue Moon here means the second full moon in one calendar month, a popular definition dating from 1946. A calendar month holds two full moons roughly every two and a half years. The older seasonal definition, the third full moon in a season with four, gives different dates and is left out of the table.

Supermoon has no official astronomical definition. This calendar marks a full moon as a supermoon when the distance between the centres of Earth and Moon is under 360,000 km at the moment of full moon. A supermoon looks about 14% wider than a full moon near apogee, a difference hard to see without a side-by-side photo.

Metonic cycle

Nineteen calendar years contain almost exactly 235 lunations, so the moon phases repeat on nearly the same dates every 19 years. The Greek astronomer Meton described the cycle around 432 BC, and the date of Easter still relies on the 19-year cycle. The full moon of 3 January 2026 returns on 3 January 2045, within half an hour.

Full moon names and eclipses

The full moon names come from North American almanac tradition, one per month from the Wolf Moon in January to the Cold Moon in December. The Harvest Moon is the full moon closest to the September equinox, and the Hunter's Moon is the one after the Harvest Moon. Eclipse markers show the type of eclipse somewhere on Earth. A solar eclipse is visible only along a narrow path or region, and a lunar eclipse is visible from the night side of Earth.

Accuracy

All values are calculated in this browser with the algorithms from Jean Meeus, Astronomical Algorithms: chapter 49 for the phase times, chapter 47 for the Moon's position and distance, chapter 48 for illumination, chapter 27 for equinoxes and solstices, chapter 38 for perihelion and aphelion and chapter 54 for eclipses. ΔT comes from the Espenak and Meeus polynomials. From 1700 to 2100 the phase times land within a minute or two of the published US Naval Observatory times, and the eclipse types match the NASA eclipse catalogue for more than 99% of eclipses. Borderline cases, such as a barely total lunar eclipse or a hybrid solar eclipse, sometimes show as the neighbouring type. Easter follows the Gregorian computus used by Western churches.