<P> 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 . </P> <P> 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 2449128.59 + 29.53058867 ∗ (B L N − 871) ± 0.25 (\ displaystyle 2449128.59 + 29.53058867 * (\ mathrm (BLN) - 871) \ pm 0.25), with the given uncertainty due to varying torques from the sun . </P> <P> 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 . </P> <P> 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 . </P>

During what period of time does the moon appear in the sky on a new-moon day