Time Scales and Coordinate Systems

Procedures are given to calculate both intermediate and apparent right ascension, declination and hour angle of planetary and stellar objects which are referred to the International Celestial Reference System. These procedures include the effects of the differences between time-scales, light-time and the relativistic effects of light deflection, parallax and aberration, and the rotations to give the "of date" system. In particular, the rotations from the Geocentric Celestial Reference System to the equator of date are illustrated using both equinox-based and Celestial Intermediate Origin-based techniques.

The printed volume includes daily tabulations of the nutation angles, Δ ψ and Δ ε, the true obliquity of the ecliptic, Greenwich mean and apparent sidereal time and the equation of the equinoxes, as well as the new parameters that define the Celestial Intermediate Reference System X, Y, s, and the Earth rotation angle, together with various useful formulae.

The Astronomical Almanac Online! 2020