Moon Phases and Moon Signs: Two Clocks, Two Questions

“It’s a full moon in Pisces.” That one sentence contains two separate pieces of information that beginners often blur together. The first, full moon, is a phase. The second, in Pisces, is a sign. They come from different parts of the Moon’s motion and they change on different schedules, and keeping them apart makes almost everything said about the Moon easier to follow.

Clock one: the phase (about 29.5 days)

The Moon’s phase is about its position relative to the Sun. The Moon reflects sunlight, and as it circles the Earth we see more or less of its lit half. When the Moon sits roughly between us and the Sun, we see the dark side: a new moon. A week later we see half of the lit side (first quarter), two weeks after the new moon we see all of it (full moon), and then it shrinks through last quarter back to new.

The full cycle takes about 29.5 days, called the synodic month. It is a little longer than the 27.3 days the Moon takes to go around the Earth once against the stars, because the Earth is also moving around the Sun and the Moon has to catch up.

Astrologically, the phase is about timing and rhythm: beginning, building, culminating, releasing, resting. You can see tonight’s phase on the Moon Calendar.

Clock two: the sign (about 2.5 days)

The Moon’s sign is about its position relative to the zodiac, the belt of stars along the Sun’s path. The Moon circles the zodiac in 27.3 days, so it spends just over two days in each sign. It changes sign roughly every two to three days.

Astrologically, the sign is about mood and flavor. A Moon in Taurus is said to favor comfort and steadiness; a Moon in Gemini, talk and variety; a Moon in Scorpio, intensity. It is the quality of the day, where the phase is the stage of the cycle.

Why the two can be combined

Because the clocks differ, every combination occurs. A new moon can happen in any sign, and so can a full moon. That is why astrologers describe a full moon as “in” a particular sign, and why two full moons a month apart feel different: the second is in a different sign. A new moon in Virgo is read as a time to organize and refine; in Sagittarius, to plan travel or learning.

In your birth chart

Your chart has both:

• Your Moon sign is where the Moon sat in the zodiac when you were born. It describes your emotional nature. It needs your birth time if the Moon changed signs on your birthday.
• Your birth Moon phase is how lit the Moon was. Astrologers in the tradition of Dane Rudhyar use it to describe your overall rhythm: a new-moon person is said to be instinctive and self-starting; a full-moon person, relational and expressive.

The Birth Moon Phase Finder gives you the phase and the sign; the Birth Chart Studio gives you the exact Moon sign when you supply a birth time.

What the evidence says about the Moon

It is worth being honest: studies of the full moon and human behavior, including sleep, births, crime and hospital admissions, have mostly not found reliable effects. A few have found small changes in sleep around the full moon, which could be due to bright nights. So the Moon’s phases are a lovely calendar, but there is no good evidence they change behavior.

A practical monthly rhythm

The use that has held up best is as a gentle planning cycle, which works whatever you believe. At the new moon, decide what the month is for. At the first quarter, check your progress and fix what is stuck. At the full moon, review and celebrate what is done. At the last quarter, let go of what did not work. In the last days, rest. The Moon page covers what it means in a chart.