Special remarks on German mountings

One should expect some ``TEOBSE'' and ``TWOBSW'' hour angles to lie near the meridian, because the telescope tends to run into the pier at declinations close to the latitude (i.e., near the zenith). There is the possibility that some telescopes cannot quite reach the zenith and may have small limits of either sign. For this reason, the minus sign cannot be optional for hour angles east, for German equatorials.

This mechanical limitation on setting the telescope may also affect the ``moonlight'' limits. Suppose the telescope is a reflector with an open tube, and can just reach the meridian when it is near the zenith. Then the Moon can only shine on the mirror (in this orientation) when it is high enough to shine in over the edge of the dome. As the lower edge of the dome is usually about the same height as the intersection of the polar and declination axes, the telescope mirror is some distance below the bottom of the dome shutter when the telescope points at the zenith. Then the Moon may have to be (say) high to illuminate the mirror, with the telescope on this side of the pier. Such considerations should be taken into account in compiling tables for German equatorials. (See Table for examples.)

In some cases (e.g., the ESO 1.5-meter), it is very inconvenient to move the telescope from one side of the pier to the other during the night. With some instruments, it may be necessary to change wiring harnesses in reversing the telescope. Because photometry requires efficient use of telescope time, these situations make reversing the telescope impractical. The best way to handle such cases is to designate the ``telescope East'' and ``telescope West'' conditions as separate foci in the observatory table file. The obvious suffixes to use are E and W. Then separate horizon-limit tables would be used for the two conditions.