The Lunation Number or Lunation Cycle is a number given to each lunation beginning from a specific one in history. Several conventions are in use. The most commonly used was 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 American Ephemeris and Nautical Almanac. More @Wikipedia
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