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A&A Supplement series, Vol. 123, June I 1997, 403-410

Received June 12; accepted September 25, 1996

Discussion of the results from solar astrolabes

J.L. Pennatex2html_wrap1615 - P. Benevides-Soarestex2html_wrap1617 - A.H. Andreitex2html_wrap1619 - F. Laclaretex2html_wrap1621

Send offprint request: J.L. Penna,Observatorio Nacional/CNPq, R. Gal. José Cristino 77, CEP 20921-400, Rio de Janeiro, e-mail:

tex2html_wrap1623  Observatorio Nacional/CNPq, Brasil
tex2html_wrap1625  Instituto Astronômico e Geofísico/USP, Brasil
tex2html_wrap1627  Observatoire de Calern/OCA, France


In this work we investigate on the stability of the results from solar observations obtained with the modified astrolabes of the Observatoire de la Côte d'Azur/France, of the Observatório Abrahão de Moraes/IAG/USP-Brazil and of the Observatório Nacional/Brazil. The mass of data is comprised of 6273 observations of both solar limbs, from 1974 to 1992, and is analyzed to determine the origin of the fundamental reference system and the Earth's orbital parameters. The solution stability was verified by checking against any large variation upon the individual weights, as well as for different sub samples of the whole set of observations. The results were also shown invariant to changes in the adopted model, such as adding unknowns to the refraction algorithm, to the time variation of the obliquity (including the nutation constant) and to the azimuthal anomalies of the refraction. In our analysis we obtain a standard deviation of tex2html_wrap_inline1603 for the combination of the observations with no bias on its distribution. It is also indicated that the Sun observations at astrolabes do not require any further atmosphere modelling complexity.

keywords: astrometry -- reference system -- Sun: general -- methods: data analysis

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