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. (May 2015)
The Lunation Number or Lunation Cycle is a number given to each lunation beginning from a certain one in history. Several conventions are in use.
The most commonly used is the Brown Lunation Number (BLN), which defines lunation 1 as beginning at the first new moon of 1923, the year when Ernest William Brown's lunar theory was introduced in the major national astronomical almanacs. Lunation 1 occurred at approximately 02:41 UTC, January 17, 1923. New moons occur on Julian Dates
, with the given uncertainty due to varying torques from the sun.
Another increasingly popular lunation number (simply called the Lunation Number), introduced by Jean Meeus, defines lunation 0 as beginning on the first new moon of 2000 (this occurred at approximately 18:14 UTC, January 6, 2000). The formula relating this Lunation Number with the Brown Lunation Number is: BLN = LN + 953.
The Goldstine Lunation Number refers to the lunation numbering used by Herman Goldstine in his 1973 book New and Full Moons: 1001 B.C. to A.D. 1651, with lunation 0 beginning on January 11, 1001 BC, and can be calculated using GLN = LN + 37105.
The Hebrew Lunation Number is the count of lunations in the Hebrew calendar with lunation 1 beginning on October 7, 3761 BC. It can be calculated using HLN = LN + 71234.
The Islamic Lunation Number is the count of lunations in the Islamic calendar with lunation 1 as beginning on July 16, 622. It can be calculated using ILN = LN + 17038.
The Thai Lunation Number is called "มาสเกณฑ์" (Maasa-Kendha), defines lunation 0 as beginning of the SouthEast-Asian Calendar on Sunday March 22, 638 (Julian Calendar). It can be calculated using TLN = LN + 16843.