Moon calendar

How the calendar is drawn

Each day shows the Moon as it is at midday where you are: how much of it is lit, which side the light is on, and a small glyph for the sign it is in. The Moon moves on through a sign in about two and a quarter days, so on some days it changes sign in the morning or the evening; the glyph is the sign at midday. The days with a new moon, a quarter or a full moon give the exact minute, in the time zone of this device.

Why the phases are not evenly spaced

A month from new moon to new moon averages twenty-nine and a half days, but the Moon’s orbit is an ellipse and it runs faster when it is near the Earth, so the stretch from new to full and from full to new can differ by most of a day. The quarters in the calendar are worked out one by one rather than added on at a fixed step, which is why they land where they do.

Perigee, apogee and supermoons

Perigee is the Moon’s nearest point in each orbit and apogee its furthest. A full moon that falls close to perigee looks about a seventh wider than one at apogee, and has taken the name supermoon; the list marks a full moon within two days of perigee. None of it changes anything on the ground beyond slightly higher tides, and this page claims nothing more.

The four moments and the phases between

New moon is the instant the Moon and the Sun stand at the same longitude on the zodiac; first quarter is ninety degrees on, full moon a hundred and eighty, opposite the Sun, and last quarter two hundred and seventy. Each of those is a minute on the clock, not a day, which is why only those days carry words. In between run the waxing crescent, the waxing gibbous, the waning gibbous and the waning crescent, which are stretches rather than moments, and the other days show them as the disc at midday.

Reading a day, with an example

Suppose a cell reads ‘Full moon 04:12’ with the glyph for Scorpio. The Moon was exactly opposite the Sun at 04:12 by this device’s clock, and at midday that day it was in Scorpio. The nights either side look almost as full: a day from the exact moment the Moon is still about ninety-nine per cent lit, which is why a full moon seems to last two or three nights. The list under the calendar gives the sign at the exact minute, so if the Moon changed sign between four in the morning and midday the two can differ, and both are right.

Void of course, and what is left out

In the tradition the Moon is void of course from its last exact aspect in a sign until it enters the next one, and electional astrology reads that stretch as a poor time to begin something. This calendar does not mark it, because its length depends on which aspects and planets are counted. The Moon page gives the current void of course with the traditional rule and explains the choice. Nor does the calendar say when to plant, cut hair or sign anything: it shows where the Moon is.

Hemisphere, time zone and date

The lit side is drawn as it looks from the northern hemisphere, unless the place kept on this device is south of the equator, when the discs are mirrored. Every time is in the time zone of this device. A full moon just before midnight in London falls after midnight further east, so two calendars printed for different places can put the same full moon on different dates. The signs are those of the tropical zodiac, as on the rest of the site.

Eclipses only happen at a new or full moon close to the Moon’s nodes, and Eclipses lists them for four years with the view from your city. The Almanac sets every new and full moon of a year beside the retrogrades and sign changes, and the Lunar return finds the monthly moment the Moon comes back to its place in your birth chart.