Descriptor for the ``horizon'' table

A character descriptor is needed to specify which of three possible formats is actually used:

MOUNTING: possible values are 'FORK', 'GERMAN', or 'ALTAZ'. 'ALTAZ' is self-explanatory; 'GERMAN' applies to ``cross-axis'' and other asymmetrical mountings that have different constraints, depending on which side of the pier the telescope tube is on. Everything else should be designated 'FORK', whether it really is a fork or yoke mount, or any other symmetrical form that is equatorially mounted and has no east-west differences like the German form (so called because it was first designed by Fraunhofer).

In the case of an alt-azimuth mounting that displays only equatorial coordinates to the user, it would be more convenient to use the 'FORK' form of table, despite the actual mounting. (This may be the case for the NTT, for example.) If only Right Ascension is provided and not hour angle, the user will have to record the local sidereal time and compute the hour angle. Even so, this will be less work, and is less likely to introduce errors, than to convert between equatorial and horizon coordinates.

Three separate table formats correspond to each of these three descriptor values. The next three subsections describe these three forms.