Moon Sign

The Moon is astrology's fastest-moving body: it travels the whole zodiac in about 27.3 days and changes sign roughly every two and a half days. That means the birth date alone isn't always enough to determine the Moon sign with certainty — if the Moon changes sign on the birth day itself, the time decides. It's calculated the same way as any planetary position, from ephemerides.

In astrological tradition, the Moon sign is linked to emotional expression, a sense of security and instinctive reactions. The classical pairing assigns self-expression to the Sun and needs and reactions to the Moon. That's an inherited interpretive model, not a psychological finding about a person.

The Moon sign shouldn't be confused with the Moon phase (new moon, full moon, etc.) — one is the position in the zodiac, the other the angle between Sun and Moon. Together, the two make up the complete picture of the birth Moon.