Lunation
Encyclopedia
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 tides.
In a lunar calendar
each month
corresponds to a lunation.
Individual lunations vary in length by several hours, because of the eccentricity of the orbit
s of the Moon and Earth
. However, the lunation is never more than 15 hours behind or ahead of a mean lunation.
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.
Lunar phase
A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
cycle (i.e., the synodic period of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
). 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 tides.
In a lunar calendar
Lunar calendar
A lunar calendar is a calendar that is based on cycles of the lunar phase. A common purely lunar calendar is the Islamic calendar or Hijri calendar. A feature of the Islamic calendar is that a year is always 12 months, so the months are not linked with the seasons and drift each solar year by 11 to...
each month
Month
A month is a unit of time, used with calendars, which was first used and invented in Mesopotamia, as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately...
corresponds to a lunation.
Individual lunations vary in length by several hours, because of the eccentricity of the orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
s of the Moon and Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. However, the lunation is never more than 15 hours behind or ahead of a mean lunation.
Correspondence with Human Female Menstrual Cycle
It has long been thought that the periodPeriodic function
In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,...
of the lunation cycle is associated with the menstrual cycle
Menstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human 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.
See also
- monthMonthA month is a unit of time, used with calendars, which was first used and invented in Mesopotamia, as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately...
- lunar phaseLunar phaseA lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
- new moonNew moonIn astronomical terminology, the new moon is the lunar phase that occurs when the Moon, in its monthly orbital motion around Earth, lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth...
, full moonFull moonFull moon lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun. More precisely, a full moon occurs when the geocentric apparent longitudes of the Sun and Moon differ by 180 degrees; the Moon is then in opposition with the Sun.Lunar eclipses can only occur at... - full moon cycleFull moon cycleThe full moon cycle is a cycle of about 14 lunations over which full moons vary in apparent size and age . The sequence is*Full moon big - *Full moon young -...
- lunar calendarLunar calendarA lunar calendar is a calendar that is based on cycles of the lunar phase. A common purely lunar calendar is the Islamic calendar or Hijri calendar. A feature of the Islamic calendar is that a year is always 12 months, so the months are not linked with the seasons and drift each solar year by 11 to...
, lunisolar calendarLunisolar calendarA lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year. If the solar year is defined as a tropical year then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year then the calendar will... - Lunation NumberLunation NumberLunation Number is a number given to each lunation beginning from a certain one in history. There are several series of lunation numbers in use....