Abstract: A laser beam from a laser beam oscillator is guided to an incidence light path of a beam splitter of a Michelson interferometer by means of a first guide mirror, reflected by a fixed mirror and a scanning mirror of the Michelson interferometer, and returned to the beam splitter, thus obtaining an interference light beam. The interference laser beam is guided to first and second laser beam detectors by means of a second guide mirror to detect variations in intensity of the interference laser beam. On the basis of the variations in intensity of the interference laser beam, an angle of inclination (.theta.) of the scanning mirror is measured.

Abstract: A star scanner according to this invention has an optical system for forming a star image, a photoelectric transducer arranged at a scanning section for the star image to be formed by the optical system, and a signal processor for generating detection data on the star image in accordance with a signal output from the photoelectric transducer. The optical detector fo the photoelectric transducer has semiconductor photosensitive elements arranged at the scanning section for the star image to be formed, and reticles, arranged between the semiconductor photosensitive elements and the optical system, to constitute a plurality of photosensitive sections and light-blocking sections on the photosensitive surface ofthe semiconductor photosensitive elements along a star image-scanning direction. The signal processor has means for generating detection data on the star image in accordance with the signal output of the semiconductor photosensitive elements.