Variations of the Solar Diameter

Details Variations of the Solar Diameter Variations of the Solar Diameter

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003ala..conf..195r&link_type=abstract

Astronomy in Latin America, Second Meeting on Astrometry in Latin America and Third Brazilian Meeting on Fundamental Astronomy,

Astronomy and Astrophysics

Astronomy

Scientific paper

This work aims to present results from the 1998 to 2000 campaign of solar diameter surveying, done at the Observatório Nacional campus. The employed instrument was a Danjon astrolabe, specially modified for the solar observations. During the time lapse, 10807 independent observation, which resulted in 9112 measurements of the solar diameter, were taken evenly distributed Eastwards and Westwards from the local meridian. A study is made to identify the systematic effects of the observational conditions. The derived corrections are of the order of hundredths of arc seconds, thus being tenfold smaller than the typical error of one observation. The mean semi-diameter for this period is found as 959.107" +/- 0.006". Through the use of a CLEAN algorithm the periodic terms of the semi-diameter were obtained. The largest amplitude is attached to that of 515 days. By using a second type of algorithm, namely the DCDFT (Ferraz-Mello, 1981), the found periods stand additional proof. A dependency of the semi-diameter on the observed heliolatitude is verified. The difference between the equatorial and polar radii was calculated as Dr = 0.013" +/- 0.004". Adopting the component of the oblateness due to surface rotation alone as dr= 7.8 mas (Rozelot & Rösch, 1997), the gravitational quadrupole moment of the Sun, is inferred as |J2|= 3.61 +/- 2.90 × 10-6.

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