Appnr

astronomical almanac - calculate planet and star positions

The aa program computes the orbital positions of planetary bodies and
performs rigorous coordinate reductions to apparent geocentric and
topocentric place (local altitude and azimuth). It also reduces star
catalogue positions given in either the FK4 or FK5 system. Data for
the 57 navigational stars is included. Most of the algorithms
employed are from The Astronomical Almanac (AA) published by the
U.S. Government Printing Office.

The aa program follows the rigorous algorithms for reduction of
celestial coordinates exactly as laid out in current editions of
the Astronomical Almanac. The reduction to apparent geocentric
place has been checked by a special version of the program (aa200)
that takes planetary positions directly from the Jet Propulsion
Laboratory DE200 numerical integration of the solar system. The
results agree exactly with the Astronomical Almanac tables from
1987 onward (earlier Almanacs used slightly different reduction
methods).

Certain computations, such as the correction for nutation,
are not given explicitly in the AA but are referenced there. In
these cases the program performs the full computations that are
used to construct the Almanac tables (references are provided).