Is the lunar calendar based on calculations a satisfactory alternative to the observation of the new moon?
The lunar calendar based on astronomical calculations has been in existence for some four millennia. It was already used by the Babylonians in the 18th c. B.C. Each lunar month begins, as was stated, at the time of the monthly “conjunction”, when the Moon is located on a straight line between the Earth and the Sun. The month is defined as the average duration of a rotation of the Moon around the Earth (29.53 days). The lunation (period of time between two successive new moons) varies within a zone whose limits are 29.27 days at the Summer solstice and 29.84 days at the Winter solstice, giving for the 12 months’ year an average length of 354.37 days. From an astronomical point of view, lunar months do not alternate between a length of 30 days and 29 days in succession. There are, at times, short series of 29 d, and at other times short series of 30 d, as illustrated by the length (in days) of the following 24 lunar months, corresponding to the period 2007-2008 : « 30, 29, 30, 29, 29, 30
