Concise Telescope Pointing Algorithm Using Iau 2000 Precepts

The accuracy requirements for pointing a ground-based telescope or antenna are comparatively modest; the latest Earth orientation models used by specialists have precision goals measured in microareseconds and are excessive for such humble applications. Abridged formulations offer an attractive alternative: easier to get right, and much quicker to compute. Moreover, the revised computational procedures that the IAU introduced in 2000 to assist high-precision studies of Earth rotation lend themselves to approximation. Together with basic models for aberration and refraction, a page of inline C code is enough to predict the observed altazimuth coordinates of a star to an accuracy of 1-2 arcseconds, which is adequate for pointing a small telescope. This can be complemented by a similarly concise formulation of the basic pointing corrections for an equatorial or altazimuth mount.