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Lunation is the mean time for one lunar phase cycle (i.e., the synodic period of the Moon). It is on average 29.530589 days, or 29 days 12 hours 44 minutes and 3 seconds. The length of this cycle is linked to many phenomena in nature, such as the variation between spring and neap tides (the extreme highest and lowest tides, respectively).
Individual lunations vary in length by several hours, because of the eccentricity of the orbits of the Moon and Earth. However, the lunation is never more than 15 hours behind or ahead of a mean lunation.
Each cycle of the phases of the Moon is given a Lunation Number to identify it.
Correspondence with Human Female Menstrual Cycle
It has long been thought that the period of the lunation cycle is associated with the menstrual cycle of mature human females. A 1979 study of 305 women found that approximately one-third of the subjects had lunar period cycles, i.e., a mean cycle length of 29.5 days plus or minus 1 day. Almost two-thirds of the subjects started their cycle in the brighter half of the lunar cycle, significantly more than would be expected by random distribution. Another study found a statistically significant number of menstruations occurred around the new moon.
- Friedmann, E (1981). "Menstrual and lunar cycles". American journal of obstetrics and gynecology 140 (3): 350. Template:Hide in printTemplate:Only in print.
- Law, Sung Ping (1986). "The Regulation of Menstrual Cycle and its Relationship to the Moon". Acta Obstetricia et Gynecologica Scandinavica 65 (1): 45–8. Template:Hide in printTemplate:Only in print. Template:Hide in printTemplate:Only in print.