A prismatic astrolabe with a micrometer, designed in 1938 by the French astronomer A. Danjon. It eliminates the observer’s personal equation in measuring the instant at which the direct and reflected images of a star coincide; hence it is also known as an impersonal astrolabe. The main prism is equilateral so that observations are made at a constant zenith distance of 30°. Danjon astrolabes have been used since the 1950s for measuring time and latitude and in observations for compiling star catalogues.
Subjects: Astronomy and Astrophysics.