New moon western horizon shortly after sunset and before moonset. A lunation or synodic month is the average time from one new moon to the next. In the J2000.0 epoch, the average length of a lunation is 29.530588 days (or 29 days, 12 hours, 44 minutes, and 2.8 seconds). However, the length of any one synodic month can vary from 29.26 to 29.80 days due to the perturbing effects of the Sun's gravity on the Moon's eccentric orbit. In a lunar calendar, each month corresponds to a lunation. Each lunar cycle can be assigned a unique lunation number to identify it. The
Lunar month Lunar month In lunar calendars, a lunar month is the time between two successive syzygies (new moons or full moons). The use of the lunar month varies by which culture has utilized the method, the main difference being when the "new" month begins. This article deals with the definitions of a 'month' that are mainly of significance in astronomy. For other definitions, including a description of a month in the calendars of different cultures around the world, see: month. In Shona, Middle-Eastern, and European traditions, the month starts when the young crescent moon becomes first visible at evening after conjunction