Moon Sign Calculator — Birth Time Optional
Calculate the Moon’s geocentric tropical longitude. If it crossed a sign boundary on your birth date, see both possibilities rather than a guessed answer.
Important: your current location may not be your birthplace. We request permission first and never send coordinates to the server. Nearby cities are suggestions, not definitive geocoding.
What happens when birth time is unknown?
We calculate the Moon’s position throughout the selected birthplace’s historical local day. If its sign stays unchanged, that sign is shown. If an ingress occurred, both signs and an approximate local crossing time are shown. You can narrow the window to a remembered part of the day. We do not invent probabilities.
Calculation method and accuracy
Uses a Meeus lunar periodic-series approximation for geocentric tropical ecliptic longitude, converting the birthplace’s civil time with the browser’s IANA historical time-zone data. Some historical records or daylight-saving transitions are ambiguous. Results very close to a sign boundary merit an authoritative ephemeris check. Supported dates: 1900–2100.
What does a Moon sign mean?
In traditional astrology, the Moon sign symbolises emotions and inner needs. This is a cultural, entertainment-only interpretation, not a scientific measure of personality or mental health. The Moon’s astronomical position itself can be independently calculated.
Method reference: Jean Meeus, Astronomical Algorithms, Chapter 47 (Moon position). Calculation runs locally; birth information is not transmitted to a third-party service.
Astrology is for entertainment and self-reflection. There is no scientific evidence that zodiac signs predict the future, personality or relationship success.