The mean time for one lunar phase cycle (i.e., the synodic period of the Moon) is 29.530589 days, or 29 days, 12 hours, 44 minutes, 3 seconds. More specifically, a lunation is also commonly defined as the mean time between successive new moons. However, as a result of torques from the Sun, the actual time interval between consecutive new moons varies greatly. Meeus (1988) gives a table of the shortest (29 days 06 hours 35 minutes) and longest (29 days 19 hours 55 minutes) lunations from 1900 to 2100.

New moons occur on Julian days

where n is an integer. The lunation number is defined such that lunation n = 1 corresponds to the first new moon that occurred in 1923. The date on which lunation n occurs can be computed using Lunation[n+284] in the Mathematica application package Scientific Astronomer, which returns results accurate to within about three minutes. The lunation number closest to a given date can be determined using Lunation[neardate]-284.

The following table gives the dates and times (in UT) for new moons in 2001-2004 computed using Scientific Astronomer.

Moon, Moon Phase, New Moon