<P> See the article on the full moon cycle for a fairly simple method to compute the moment of new moon more accurately . </P> <P> The long - term error of the formula is approximately: 1 cy seconds in TT, and 11 cy seconds in UT (cy is centuries since 2000; see section Explanation of the formulae for details .) </P> <P> The moment of mean conjunction can easily be computed from an expression for the mean ecliptical longitude of the Moon minus the mean ecliptical longitude of the Sun (Delauney parameter D). Jean Meeus gave formulae to compute this in his popular Astronomical Formulae for Calculators based on the ephemerides of Brown and Newcomb (ca . 1900); and in his 1st edition of Astronomical Algorithms based on the ELP2000 - 85 (the 2nd edition uses ELP2000 - 82 with improved expressions from Chapront et al. in 1998). These are now outdated: Chapront et al. (2002) published improved parameters . Also Meeus's formula uses a fractional variable to allow computation of the four main phases, and uses a second variable for the secular terms . For the convenience of the reader, the formula given above is based on Chapront's latest parameters and expressed with a single integer variable, and the following additional terms have been added: </P> <P> constant term: </P>

How do you know when it's a new moon