NavList:

Hi,

As the Julian Day Number (JDN) plays an important role in the computation of astronomical and nautical ephemerides it may be useful to point out that several JDN algorithms were developed in the 1960s and 1970s.

The Fliegel & Van Flandern (1968) algorithm, online here

  https://dl.acm.org/doi/pdf/10.1145/364096.364097

and mentioned a few days ago was popularized in the astronomical literature in a revised formulation by Van Flandern & Pulkkinen in their 1979 paper on the computation of low-precision ephemerides for the Sun, the Moon and the planets

  https://ui.adsabs.harvard.edu/abs/1979ApJS...41..391V

How (and why) these algorithms work is far from obvious but an alternative algorithm published by Robert G. Tantzen in 1963 and online here

  https://dl.acm.org/doi/pdf/10.1145/366707.390020 (cf. algorithm 199)

is much easier to understand.

This algorithm was popularized in the astronomical literature by Jean Meeus in a 1977 paper in a Belgian astronomical journal, online here

  https://ui.adsabs.harvard.edu/abs/1977C%26T....93..158M

and in the various editions of his _Astronomical Formulae for Calculators_ (first English edition published in 1979).

A partial explanation of Tantzen's algorithm can be found in a 2003 paper by Paul H. Kimpel, online here

  https://www.digm.com/Resources/Gregory/Date-Manipulations-in-WFL.pdf

Rob van Gent