THE PROBLEM OF THE SIGHTING LINE STABILIZATION FOR AXIAL MERIDIAN CIRCLES

The paper deals with the method based on treating the axial meridian c ircle and a long-focus light mark in the prime vertical as a single vi rtual instrument that has properties of meridian circle. A horizontal axis, a sighting line, and a micrometer cross-wire of the instrument a re created by optical means. The key function here is performed by the light mark that ensures a reference direction used for formation of i nstrumental principal planes and directions. Stability of instrumental azimuth, inclination, and collimation is expected to be about +/-0.'' 01. Besides, an accuracy of observations is not affected by any temper ature and weight deformations of telescope mechanics. Owing to the las t circumstance, the design is cheap and the telescope aperture may be increased significantly, to about 1m. An estimate of accuracy, of obse rvations depends on the adopted model of image motion, and for sites w ith excellent seeing and bright stars is +/-0.''03 to +/-0.''05 (rms).