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 day daylight at a given point on the Moon would last approximately two weeks from beginning to end, followed by approximately two weeks of night. In some lunar calendars, such as the Hindu calendar, a lunar day, or "tithi", is defined as 1/30th of a lunar month, or the time it takes for the longitudinal angle between the Moon and the Sun to increase by 12 degrees. By this definition, lunar days generally vary in duration. Lunar day A lunar day is the period of time for Earth's Moon to complete one rotation on its axis with respect to the Sun.