Lunar Phase Cycle

The changing phases of the moon form the most obvious regular cycle of events in the night sky. This phase cycle of the moon, known by astronomers as the synodic month and also as a lunation, is between twenty-nine and thirty days long. The details depend upon the viewer's latitude on earth, the time of year, and upon the timing in relation to certain longer-term cycles of the moon, but generally the phase cycle adheres to the following pattern. After a period of no more than a few days when the moon is not seen at all, a thin crescent moon is seen low in the western sky just after sunset, following the sun downward. During the next few nights, the moon grows in phase night by night and also appears higher in the western sky night by night, taking longer until it sets. By the time half phase is reached, also known confusingly as first quarter, since this is a quarter of the way through the cycle, the moon appears close to the north-south meridian at dusk and sets approximately halfway through the night. During the next seven days it becomes gibbous. It now appears in the eastern sky at dusk, or may even be visible before dusk, taking most of the night to pass at first across the meridian and then set in the west in the early hours. Finally, the moon becomes full. The full moon rises around dusk and sets around dawn. Then, during the next seven days, while it decreases back to half phase, it rises progressively later each night and is still high in the western sky at dawn. By the time half phase (third quarter) is reached, it rises approximately halfway through the night and reaches the meridian around dawn. Then finally, as it diminishes back to a crescent, it rises progressively later and later, getting less and less far up into the eastern sky by dawn, until finally the thin crescent is seen only briefly just before sunrise.

The lunar phase cycle is likely to have been recognized by human communities well back into Palaeolithic times. One obvious practical consequence of the changing lunar phases is that at certain times in the month one can see to travel about at night, when hunting, for example. Seafaring communities could also become aware that the appearance of the moon is related to the tides. The fact that the length of the phase cycle is close to that of the female menstrual cycle has led to controversial suggestions that groups of women in hunter-gatherer communities would tend to synchronize their menstrual periods not only with one another but also with the phases of the moon. This, alongside the other effects, could lead to the regulation of food gathering, fishing, hunting, cooking, feasting, and sexual activity—all in accordance with the moon. And this cycle, in turn, would eventually become "institutionalized," reinforced through ritual practices and taboos related to the lunar phases, and encapsulated in myth. Although this sequence of events is speculative, examples abound of the influence of the lunar cycles on human activity. Indigenous peoples in the historical and modern world often tied ritual practices to the phases of the moon (the Hawaiian calendar is just one example), and many folk practices and beliefs relate to the lunar phase cycle, such as those found in the Baltic states of Lithuania and Latvia.

See also:

Hawaiian Calendar.

Meridian; Moon, Motions of.

References and further reading

Aveni, Anthony F. Stairways to the Stars: Skywatching in Three Great Ancient Cultures, 28-32. New York: Wiley, 1997.

-. Skywatchers, 67-71. Austin: University of Texas Press, 2001.

Knight, Chris. Blood Relations. New Haven: Yale University Press, 1991.

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