Dark moon

The duration of a dark moon varies between 1.5 and 3.5 days, depending on its ecliptic latitude.

When the Moon's orbit is divided into 30 segments, as the ancient Greeks did in the time of Homer, the Babylonians did, and the Indians still do today (calling them tithi), the last phase is called the "dark moon".

This 12° arc is called uma by the Babylonians and tithi by the Indians.

The Moon takes a mean duration of 23 hours and 37 minutes to cover this length, but this period can vary from 21 to 26 hours because of the Moon's orbital anomaly.

This means that the "dark moon" actually lasts approximately 23 hours and 37 minutes and includes any time marked as "new moon" on a lunar calendar, and not 1.5 to 3.5 days as stated earlier.