Moon sign calculator: what is my moon sign?

Your Moon sign is the sign of the zodiac the Moon was passing through at the moment you were born. Your Sun sign describes the self you grow into; in astrology the Moon describes what you need in order to feel safe: your emotional reflexes, your habits and the way you comfort yourself when things go wrong.

Astrologers read the Moon together with the Sun and the rising sign, the trio known as the big three. This page covers the Moon on its own, with more detail than a big three reading has room for: the exact degree, the phase of the Moon at your birth, and what happens when the Moon changed sign on your birthday.

The Sun spends about a month in each sign, so a birthday is enough to name it. The Moon is the fastest body in the sky. It moves between about 12 and 15 degrees a day and crosses a whole sign of 30 degrees in about two to two and a half days, so it goes around the whole zodiac in 27.3 days.

That speed means that on roughly four days in ten the Moon changes sign at some point during the day. On those days the birth time settles the sign, and so does the local date. This calculator works in the time zone of your birthplace, with the offset and daylight saving time that were in force on the day, so a birth in Istanbul or New York keeps its own calendar date and lands on the right side of the change.

If you leave out the birth time, the calculator looks at the whole local day, from midnight to midnight. When the Moon stayed in one sign, your Moon sign is certain and only its degree is an estimate. When the Moon crossed into the next sign, you see both signs and the time of the crossing, to the minute, in your birthplace's local time.

The calculator shows both signs side by side. A birth certificate, a hospital record or a parent's memory of morning or evening is often enough to settle which one is yours. If your recorded time sits within a few minutes of the change, treat it with some caution, because birth times are often rounded to the nearest quarter hour. Reading both short descriptions can help too: many people recognize their Moon at once.

The Moon's position comes from the lunar theory in Jean Meeus's Astronomical Algorithms, the truncated ELP2000-82 series, corrected for nutation to give the apparent longitude of date. Signs are tropical, measured from the spring equinox, as in Western astrology. The time of each sign change is found by narrowing the search down to the second, and in our checks against NASA JPL's Horizons ephemeris those times agree to within about ten seconds; the accuracy page shows the comparison.

Your place is turned into coordinates and a time zone, and your local clock time into Universal Time using the historical rules of that zone. The whole calculation runs in your browser. To show the first line of today's reading, your birth details are sent once to our server, which does not store them; the place search sends only the place name you type.

The result also shows the phase the Moon was in, from the angle between the Moon and the Sun: how much of the disc was lit and whether the light was growing or shrinking. A birth near the new moon happens with the Moon close to the Sun, a birth near the full moon with the Moon opposite it.

Astrology reads the birth phase as a second layer on top of the sign. People born under a waxing Moon are said to build and reach outward, while those born under a waning Moon tend to reflect, refine and let go. That reading is symbolic, and our guide to the phases of the Moon keeps it clearly apart from the astronomy of each phase.

The big three calculator puts your Moon sign beside your Sun and rising sign, and the rising sign calculator finds the one that needs the exact time. Sun, Moon and rising explained compares the three in plain terms.

To see the Moon as it is today, open the lunar calendar; the moon phases guide explains the cycle. The calculator reads your birth date and time in your birthplace's own clock, and why charts differ explains how that clock, the zodiac and the house system shape any chart.