Astrolabe zenith distance variation

Details Astrolabe zenith distance variation Astrolabe zenith distance variation

May 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984a%26a...134..338b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 134, no. 2, May 1984, p. 338-342. Research supported by the Fundacao de Amparo

Astronomy and Astrophysics

Astrophysics

9

Astrolabes, Astrometry, Distance Measuring Equipment, Instrument Errors, Zenith, Error Analysis, Least Squares Method, Prisms, Time Dependence

Scientific paper

This paper is concerned with the problem of the zenith distance stability in the Danjon (1958) prismatic astrolabe, and with practical means to control its variations. A full description of the experimental measurements of the thermal gradient along the prism with help of the shape by autocollimation is given. The estimation of the available temperature readings is also considered. The zenith distance dependence on time, as a consequence of the prism thermal radiation towards the sky, is discussed and an interpolation model for instantaneous values between the measurements is given. Application of both the autocollimation and temperature estimates to the determination of systematic differences in radius between successive groups is considered in detail. Two sets of solutions, by least squares and by the chain method, are given and shown to be equivalent. It is also shown that the prism deformation essentially keeps the diedral surface curvatures unaltered. The radius difference estimates display an accuracy of the order of 0.15 arcsec for the autocollimation method and of 0.11 arcsec for the temperature method.

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