Equal Altitude Instruments

Abstract

The meridian plane is not the only surface which can be realized by an astronomical instrument as a reference to determine the times at which it is crossed by stars in order to deduce information on their position. For instance, there have been attempts to observe in the prime vertical (East—West vertical plane), but they were unsuccessful because they present the same technical problems as the meridian circles and, in addition, the number of stars accessible is much smaller, the star image does not transit perpendicularly to the plane and the instrumental parameters are much more complicated to determine. All this is due to a strongly asymmetrical geometry.