Lunar month

What is a lunar month?

A lunar month, or lunation, is the cycle from one new moon to the next. Its mean length is about 29.5 days, so it does not line up cleanly with Gregorian calendar months. Some calendar months contain one new moon, some contain two, and a new moon near the edge of a month can make the visible pattern feel shifted by several days. That is why a lunar month is best read as a continuous cycle rather than as a named page on the wall calendar.

This tool treats the lunar month as an astronomical cycle, not a civil month. Day 1 starts at the instant of the new moon, when the Moon is nearly between Earth and the Sun. Around the middle of the cycle the Moon reaches full phase, then wanes back toward the next new moon. Because the Moon's orbit is elliptical and tilted, each lunation is a little shorter or longer than the average. The displayed daily grid uses the UTC date containing each noon in the cycle, so it is meant for planning and comparison rather than for legal or religious calendar boundaries.

The zodiac sign shown for each new moon is approximate: it uses the Sun's tropical ecliptic longitude divided into twelve 30-degree segments. That is an astronomical convention for locating the Sun along the ecliptic, not a claim about astrology. For moonrise, moonset, and location-specific viewing details, use the moon phase calendar. Together, the two tools answer different questions: this page explains the shape of the whole lunation, while the phase calendar answers what the Moon looks like and when it clears the horizon from a chosen place.