Astron. Astrophys. 343, 1001-1004 (1999)

Heliographic latitude dependence of the apparent solar radius

F. Noïl

Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Received 27 October 1998 / Accepted 9 December 1998

Abstract

A brief outline is given of the advantages of the drift scan method and of the Danjon astrolabe for measuring the apparent solar radius. An analysis of 2111 measurements of the apparent semidiameter of the Sun made with a modified Danjon astrolabe at Santiago, Chile, shows a significant dependence of the observed semidiameter with the heliographic latitude. These results are confirmed by similar data obtained at the northern hemisphere with the solar astrolabe of CERGA, France. On the average the results of Santiago and CERGA show a maximum value of the semidiameter around solar latitude and two minimums at and . The amplitude is . The results of both astrolabes show a rather clear anticorrelation with non facular temperature excess along the solar limb. The temperature data were obtained by other authors from observations made with the Princeton Solar Distortion Telescope.

Key words: astrometry Sun: fundamental parameters

Send offprint requests to: F. Noïl

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Contents

• 1. Introduction
• 2. Solar observations with astrolabes
• 3. The solar program of the astrolabe of Santiago
• 4. Results
• 5. Discusion
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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