Moon phases, January 1946

The lunar cycle behind the calendar

The Moon's phases come from a changing angle, not from Earth's shadow. As the Moon orbits, the Sun always lights half of it, and from Earth we see a growing or shrinking share of that lit half. The cycle from one New Moon to the next is the synodic month, about 29.53 days on average. It is longer than the Moon's actual orbit around Earth (the sidereal month, about 27.32 days) because Earth moves along its own orbit in the meantime, so the Moon needs a little over two extra days to catch up with the Sun again.

Because 29.53 days does not divide evenly into a year, a calendar year holds 12 or occasionally 13 Full Moons, and the phases fall on different dates every year. The individual months also vary: depending on where the Moon is in its elliptical orbit, a synodic month can run from roughly 29.3 to 29.8 days, so the gap between two Full Moons is never quite the same.

How the phases are calculated

The calendar lists four exact moments per cycle, defined by the angle between the Moon and the Sun along the ecliptic: 0° for the New Moon, 90° for the First Quarter, 180° for the Full Moon and 270° for the Last Quarter. Each moment is found to under a second and shown in your chosen time zone, together with the sign and degree of the Moon at that instant.

Between these four points lie the in-between phases: waxing crescent, waxing gibbous, waning gibbous and waning crescent. Together they make the eight phases you may see named elsewhere on the site, each spanning 45° of the Sun–Moon angle. The difference matters: the four main phases are moments, while the eight-phase names describe stretches of three to four days. The day-by-day view on the 1946 calendar shows how much of the disc is lit and which sign the Moon is in for every day, which bridges the two.

A practical detail: at the exact New Moon the Moon stands at the same longitude as the Sun, so it is always in the Sun's sign, while at the exact Full Moon it is in the opposite sign. So the New Moons of a year move through the zodiac roughly one sign per month, following the Sun.

Working with the phases

Many people use the lunar cycle as a simple planning rhythm. A common practice is to write down one or two clear intentions in the day or two after the New Moon, check what has moved at the First Quarter, look honestly at the results around the Full Moon, and clear out what is finished during the waning half. The sign of the New Moon suggests the theme to focus on, and the house of your birth chart where it falls shows the area of life it touches.

Keep it modest. A phase does not guarantee an outcome, and starting something two days after a New Moon is not a mistake. The value lies in the regular pause the cycle gives you, not in hitting the exact minute.