Methodology

Everything on this site that is a number comes from calculation, not from copied tables: the phase of the Moon and how much of it is lit, the moments of full moons and new moons, the Moon’s sign and the times it changes, its distance from Earth, and the circumstances of eclipses. This page sets out the sources and the conventions, so that any figure here can be checked. Everything on this site that is a tradition is labeled as one; the last section explains how those layers are handled.

Sources

Positions of the Moon and the Sun are computed with the open-source Astronomy Engine library, which implements the standard VSOP87 planetary theory and a lunar theory accurate to about one arcminute, enough to fix the moments of phases, sign changes, and eclipses to within a minute or so. The results are computed for every day from 1900 to 2100 and cross-checked against the published lists of NASA, the US Naval Observatory, EarthSky, and the almanacs for full moon dates, supermoons, Blue Moons, and eclipses. Where this site and such a list disagree by a day, the cause is almost always the time zone, explained next.

The reference time: UTC

Every time on this site is given in Coordinated Universal Time (UTC), labeled as such, and your browser adds your local time next to it. The calendar day of an event is its UTC date. A full moon at 2:30 AM UTC on the 26th is the full moon of the 25th for readers in the Americas and of the 26th for everyone east of the Atlantic; the pages state the UTC moment, and the local time beside it tells you which day it is for you. The daily values on each date page—the phase, illumination, sign, and distance—are taken at noon UTC on that date.

Phases

The moment of a new moon, first quarter, full moon, or last quarter is the moment when the Moon’s ecliptic longitude, seen from Earth, is exactly 0, 90, 180, or 270 degrees ahead of the Sun’s. The date of each is the UTC date of that moment. The eight phases shown on the pages are assigned day by day: the four principal phases on the day of the exact moment, and the stretches between them as waxing crescent (between new moon and first quarter), waxing gibbous, waning gibbous, and waning crescent according to that difference at noon UTC. Illumination is the fraction of the Moon’s disk lit by the Sun at noon UTC, rounded to the nearest percent. The lunar day counts days from the last new moon: day 1 begins at the moment of the new moon, and the count at noon UTC is the day shown.

Moon signs

The Moon’s sign is its position in the tropical zodiac, the one used in Western astrology: the ecliptic is divided into 12 signs of 30 degrees starting from the point of the March equinox, and the Moon’s geocentric ecliptic longitude decides the sign. The sign shown for a day is the sign at noon UTC, which is the sign that holds for most of the day; when the Moon changes sign during a day, the exact time of the change is listed. The calculators take the sign at the exact moment you enter, converted from your time zone to UTC with the historical rules of that zone, including daylight saving time as it applied at the time.

Full moon names, Blue Moons, and the Harvest Moon

The names follow the convention of the American almanacs: Wolf Moon in January, Snow Moon in February, and so on to the Cold Moon in December. The Harvest Moon is the full moon closest to the September equinox, which can fall in September or October; when it falls in October, September’s full moon is the Corn Moon and the following full moon takes the name Hunter’s Moon, so a year can be without a Beaver Moon. A Blue Moon is reported under both definitions in use: the monthly one, a second full moon within a calendar month in UTC, and the seasonal one, the third full moon of an astronomical season that has four. The named moon pages list which years carry which name.

Supermoons and micromoons

A supermoon here is a full moon that falls within 10% of the Moon’s closest approach to Earth in that orbit, the definition introduced by the astrologer Richard Nolle and used by most media lists: in each lunar orbit, if the full moon’s distance is no more than the perigee distance plus a tenth of the difference between apogee and perigee, it counts. A micromoon is the mirror case at the far end of the orbit. Distances are measured between the centers of Earth and the Moon and given in miles first, with kilometers in parentheses. This definition reproduces the lists published by NASA and EarthSky; stricter definitions, such as a fixed limit of 223,694 miles (360,000 km), give a shorter list.

Eclipses

Solar and lunar eclipses are computed for the whole Earth, with the type, the maximum, and the times of each stage in UTC, and the local circumstances are computed for 18 cities on six continents, with the eclipse’s altitude above the horizon and, for solar eclipses, the fraction of the Sun covered at the city. Penumbral lunar eclipses, in which the Moon only passes through Earth’s outer shadow and dims slightly, are listed on the year pages as faint shading and are not counted on the eclipses hub. Advice on watching a solar eclipse is given plainly: look at the Sun only through proper eclipse glasses or by projection, at every stage except the brief totality of a total eclipse.

Calculators

The moon sign calculator and the moon phase calculator convert the date and time you enter from the time zone you choose to UTC and look up the Moon at that moment. Without a time of birth, the moment used is noon in that time zone, and if the Moon changed sign during that calendar day the result names both signs and the time of the change. The phase calculator reports the phase, illumination, lunar day, and distance at noon UTC on the UTC date of that moment, the same values as the date pages.

Garden, hair, food, and the body

These layers are the lunar tradition as it has been handed down in the almanacs and calendars of Europe and North America, written for this site and labeled as tradition on every page. The planting calendar uses the phase and the element of the Moon’s sign: earth signs make root days, water signs leaf days, air signs flower days, fire signs fruit days, and the days of the new moon, the full moon, and perigee are rest days. The four kinds of day come from the biodynamic sowing calendar of Maria Thun, which follows the Moon through the actual constellations; this site uses the signs of the tropical zodiac, so the same kind of day usually comes about two days later in her calendar than here. Seasonal advice is written for the temperate zone of the Northern Hemisphere with a note for readers south of the equator. The hair calendar follows the rules of the Central European tradition: the waxing Moon for growth, the waning Moon for a lasting cut, Leo and Virgo as the favored signs, Cancer and Pisces as the days to skip, and no cut or color on the day of a new moon or a full moon. The food and body texts describe what the tradition associates with each sign and phase; they make no medical claims, do not time treatment by the Moon, and are not a substitute for care. That framing is stated here once rather than repeated on every page.

Corrections

The pages are updated whenever the calculations or the texts change, and the date of the last revision is shown on the articles. If a figure on any page disagrees with a reliable published source, the contact page says how to report it; the discrepancy is checked, and the page is corrected where it is wrong.