Ephemerides calculation for comets and minor planets

Calculation of unperturbed ephemerides with arbitrary eccentricity for comets and minor planets

The Comet program calculates ephemerides of comets and minor planets on the basis of the two-body problem. Perturbations of the body under consideration by other planets are not taken into account. This simplification generally suffices for most practical applications. In comparing the results given by this program and those from other sources, however, we must remember that the data given in the
latter may not have been calculated with the same assumptions. The user does not have to bother with the type of orbit (ellipse, parabola, or hyperbola). Comet recognizes this from the given eccentricity and chooses the appropriate method of calculation. Elongated, high eccentricity ellipses are handled by the mathematically sound method devised by Stumpff.
Comet calculates heliocentric ecliptic and geocentric equatorial coordinates. In both cases, precession to the required equinox is taken into account. In addition, the geocentric coordinates are corrected for light-time effects. Geocentric coordinates in this form(including precession and light-time effects) are designated astrometric coordinates. They are directly comparable with positions in a star catalog, or may be used to plot the position of the object on a star chart with the same equinox!
In comparing the results with other sources, it is important to check whether the latter do really give astrometric coordinates with the same equinox, or even if perhaps they are apparent coordinates (in which nutation and aberration are also taken into account).
Reference:
O. Montenbruck, T. Pfleger, "Astronomy on the Personal Computer", Springer Verlag, Heidelberg, 2000.