Moon phase

Meaning

The Moon shines by the Sun’s light, and how much of its face we see lit depends on where it stands from the Sun. Astrology measures that by the Moon’s lead on the Sun along the zodiac, from 0° to 360°. At 0° the two are together and the Moon is dark: the New Moon. At 90° it is half lit, the first quarter; at 180°, opposite the Sun, it is full; at 270° it is half lit again, the last quarter. The whole round, a lunation, takes about 29½ days.

Tradition reads the lunation as a cycle of growth. The New Moon is a seed and a beginning, the waxing half a time of building, the Full Moon a peak where things come to light, and the waning half a time of sharing, sorting and letting go. Each phase is read as a quality of time, not as a promise of events.

In a birth chart, the phase the Moon was in is read as a temperament: a person born under a waxing Moon is often described as reaching forward, one born under a waning Moon as drawing meaning from what already exists.

In practice

• The four main phases are the New Moon, the first quarter, the Full Moon and the last quarter. Many people choose a New Moon to set an intention and a Full Moon to take stock.
• The eight phases divide the cycle into 45° steps: new, crescent, first quarter, gibbous, full, disseminating, last quarter and balsamic. Dane Rudhyar described them in 1967, and many modern astrologers read the birth phase this way.
• Eclipses are New and Full Moons close to the Moon’s nodes, where its path crosses the Sun’s: see eclipse.
• The sign and house of a New or Full Moon show where in a chart its theme is read to fall.

Across traditions

• Indian astrology counts thirty lunar days, the tithis, each 12° of the Moon’s lead on the Sun. The tithi of birth is part of the daily almanac, the panchanga, and guides the choice of times.
• The Chinese calendar starts each month on the day of the New Moon, and its New Year falls on a New Moon in late January or February.
• The Babylonian and Islamic calendars start the month with the first thin crescent seen after sunset.

Origin and history

Lunar months are among the oldest calendars, and the Moon’s phases among the first rhythms of the sky to be counted. Ptolemy used the New or Full Moon that came before a birth, the prenatal syzygy, to help fix the degree rising, and read the one before each equinox and solstice for the season to come. In the twentieth century Dane Rudhyar turned the lunation into a psychological cycle of eight phases, the form most modern readings follow. The share of the disc that is lit is a matter of geometry, which Jean Meeus gives as half of one plus the cosine of the phase angle, the angle at the Moon between the Sun and the Earth.

How Ulune calculates it

• In the Table, the Chart part gives the birth phase: one of the eight 45° phases, the Moon’s lead on the Sun, the share of the disc lit and whether the Moon is waxing or waning. The lit share comes from the phase angle, found from the true elongation (the Moon’s latitude included) and the mean distances of the Sun and the Moon, as the Swiss Ephemeris does. Without a birth time it is marked ~.
• In the Calendar, the four main phases are exact moments: the Moon 0°, 90°, 180° or 270° past the Sun, sampled every twelve hours and refined on the ephemeris to the millisecond. Each is given with the Moon’s degree and, when a chart is open, the house it falls in.
• On the other days the Calendar names the Moon waxing crescent, waxing gibbous, waning gibbous or waning crescent, by the quarter of the cycle it is in, with a lit share taken from the elongation alone.
• Eclipses come from the Swiss Ephemeris’s own searches, and are shown with the phase they fall on.

Correspondences