The calculated times are in Terrestrial Dynamical Time (TDT or TT), a replacement for Ephemeris
Times (ET). Meeus claims the error is less than one minute for the years 1951-2050 for these
calculations (the errors increase as you move farther away from these dates).
The algorithms and correction tables for the equinox/solstice calculations come directly from
the book Astronomical Algorithms Second Edition by Jean Meeus, ©1998, published by
Inc., Richmond, VA,
The code for the Moon phase computation appeared in Astronomical Computing,
Sky & Telescope, March, 1985,
while the code for Julian Day to Calendar Dates appeared in the same column in May 1984. In both
cases, the Basic code by Roger W. Sinnott was based on algorithms by Jean Meeus in
Astronomical Formulae for Calculators
The Basic source code was obtained from the
Sky Publishing Web Site.
The TDT to UTC corrections are from a subsequent book by Meeus:
Astronomical Algorithms, Second Edition
In all cases, the calculation routines were coded in PHP and built into this web page by the
e.Librarian at the Rudolf Steiner Archive & e.Lib.
While the output has been spot checked for correctness against known tables, the code has not been
thoroughly tested and could contain errors. The underlying algorithms are not exact and times could
vary by several minutes. Consult the book credited above for detailed information.
Note also that the day-of-week will not be correct when the date is in the Julian calendar (earlier