← Encyclopedia of Astrology · lesson 141/235
The lunation cycle
What it is
The lunation cycle is the Moon's monthly round with the Sun. The Moon moves about thirteen degrees a day and the Sun about one, so the Moon keeps catching up with the Sun, passing it and pulling away again. One full round, from one New Moon to the next, takes about 29½ days (29.53 on average), the period astronomers call the synodic month.
What we see as the Moon's phases is simply this relationship made visible. The Moon has no light of its own; the lit part we see depends on the angle between the two lights. At the conjunction the lit side faces away from us and the Moon is dark. As the angle opens, a thin crescent appears in the evening sky; at 90° we see a half Moon; at 180°, the Full Moon, the whole face is lit; then the light shrinks back until the next conjunction.
The first half, as the light grows, is the waxing Moon; the second half, as it shrinks, is the waning Moon.
The four quarters
The oldest way of dividing the cycle is into four, at the four moments everyone can see: New Moon, first quarter, Full Moon and last quarter. Ptolemy gave each quarter a quality. In her waxing from the New Moon to the first quarter, he wrote, the Moon is more productive of moisture; from the first quarter to the Full, of heat; from the Full to the last quarter, of dryness; and from the last quarter to her disappearance, of cold. Later writers matched these four to the four seasons and the four humours, so the lunar month became a small year. Lilly works with the plainer half of the scheme: a Moon increasing in light counts in her favour, and one decreasing in light against her.
The eight phases
In the twentieth century Dane Rudhyar argued that four divisions were not enough, and divided the cycle into eight phases of 45° each, measured by how far the Moon stands ahead of the Sun. Each phase begins at a key angle and runs to the next:
| Phase | Moon ahead of the Sun |
|---|---|
| New Moon | 0°–45° |
| Crescent | 45°–90° |
| First quarter | 90°–135° |
| Gibbous | 135°–180° |
| Full Moon | 180°–225° |
| Disseminating | 225°–270° |
| Last quarter | 270°–315° |
| Balsamic | 315°–360° |
Each phase lasts about three and a half days. Rudhyar read the whole round as one process, like a plant's year: a seed impulse at the New Moon, a struggle to establish it in the crescent, a crisis of action at the first quarter, refinement in the gibbous phase, illumination at the Full, sharing in the disseminating phase, a crisis of meaning at the last quarter, and a letting-go in the balsamic phase that prepares the next seed.
Two cautions about names. Astronomers and calendars use a different eightfold set — New, waxing crescent, first quarter, waxing gibbous, Full, waning gibbous, last quarter, waning crescent — and usually treat the quarters as moments, or as spans centred on them, rather than as spans that begin at them. Rudhyar's phases begin at each angle. So the same Moon can be "waxing gibbous" in a calendar and still in Rudhyar's "first quarter" phase. Neither is wrong; they answer different questions.
The phase you were born in
Rudhyar called the phase at birth a person's lunation birthday, and the eight phases lunation types. It recurs every month, when the Sun and Moon return to the same angle, and he held it to describe how a person meets life, as the Sun sign describes what they are. A waxing-phase birth is read as more instinctive and outgoing, building something new; a waning-phase birth as more reflective, working with what has already been lived. It is one strand among many, a tone and not a verdict; astrologers such as Tracy Marks and Michael Erlewine carried the idea into wide use.
To find it, measure from the Sun forward, in the order of the signs, to the Moon. A Moon 100° ahead of the Sun is in the first quarter phase; one 300° ahead (60° behind) is in the last quarter phase.
Other uses
- Elections. Electional astrology has long preferred a Moon increasing in light for anything meant to grow.
- Progressions. In secondary progression the progressed Sun and Moon make their own cycle of about thirty years, and its phases are read as chapters of a life.
- Eclipses. A New or Full Moon near the Moon's nodes is an eclipse.
In a reading here
A natal reading here names the lunation phase you were born in, using Rudhyar's eight 45° phases. A progression reading names the progressed phase and how far you are into that roughly thirty-year cycle. The Almanac shows the day's Moon phase and how much of the disc is lit, using the astronomical names, and electional readings note whether the Moon is waxing or waning.