Solar diameter observations with the Astrolabe at Observatório Nacional - Rio de Janeiro

¹ Observatório Nacional/CNPq, Brasil
² Pulkovo Observatory, Russia
³ DANOF/Observatoire de Paris, France
⁴ CERGA/Observatoire de la Côte d'Azur, France

Corresponding author: Send offprint request to: E.G. Jilinski, Observatório Nacional/CNPq, R. Gal. José Cristino 77, CEP20921-400, Rio de Janeiro, Brasil. e-mail: jilinski@on.br

Received: 24 September 1997
Accepted: 24 November 1997

Abstract

Observations of the solar diameter are reported from the astrolabe station at Observatório Nacional. All the observations presented here were taken with the 1986-CERGA prototype of Variable Prism, which enables many diameter measurements per day and to observe all year round. The 1996 DANOF software for digital CCD image acquisition and data processing has been used. We adopted the recording of 46 CCD frames with direct and reflected images of the limbs along the Sun's transit through the almucantar. The independent observable is the accurate UT datation of each frame. Here the first campaign results, from January to July/1997, are presented. An asymmetry between the east and west transit is noticeable. The west transit leads to a larger value for the mean semi-diameter and exhibits a larger standard deviation. No clear dependence is found upon the daily results, either on time or on observational parameters. The main outcome of this campaign remains the average solar semi-diameter, from 1149 transits (863 East and 286 West), obtained as 95921 ± 003.