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Title:
Solar Astrometry with the Astrolabe of Santiago
Authors:
Noël, F.
Affiliation:
AA(Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile)
Publication:
The Sun's Surface and Subsurface: Investigating Shape. Edited by J.-P. Rozelot., Lecture Notes in Physics, vol. 599, p.181-195
Publication Date:
00/2003
Origin:
SPRINGER
Comment:
ISBN: 3-540-44188-3
Bibliographic Code:
2003LNP...599..181N

Abstract

A report is given on the program of solar astrometry with a Danjon astrolabe, in progress since 1990 at Santiago, Chile. This program was envisaged as a contribution to the improvement of the orbital parameters of the Earth-Moon system and to research an eventual difference between the stellar and the dynamical equinox. However, the most interesting aspect of the results obtained so far concerns the apparent semidiameter of the Sun. More than 2800 homogeneous measurements of the solar radius have been obtained from observations at mathrm{30(°}) and mathrm{60(°}) zenith distances. The observed semidiameter at both zenith distances shows a systematic variation in time correlated with the solar activity. A significant heliographic latitude dependence of the apparent semidiameter was also disclosed. The solar radius has a maximum value around mathrm{±50(°}) heliographic latitude and two minima around mathrm{± 25(°}) and mathrm{± 75(°}) . The amplitude is mathrm{0. "07± 0. "02}.
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