Issue |
A&A
Volume 413, Number 2, January II 2004
|
|
---|---|---|
Page(s) | 725 - 732 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20031573 | |
Published online | 18 December 2003 |
Solar cycle dependence of the apparent radius of the Sun
Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
Corresponding author: fnoel@das.uchile.cl
Received:
19
May
2003
Accepted:
4
September
2003
Visual astrometric observations of the Sun covering the second and first part
of solar cycles 22 and 23 respectively, have been carried out during the last
13 years with the Danjon astrolabe of Santiago, Chile. These observations give,
among other solar parameters, an absolute value of the Sun's apparent radius.
We report here the results obtained from 4092 homogeneous radius measurements
at and
zenith distances. The data set
shows at both zenith distances a significant radius variation in phase with
magnetic activity. Moreover, the observations at
, which
are less affected by atmospheric noise, give a significantly higher
correlation coefficient between radius variation and sunspot numbers. Other
investigations of solar radius variations during the last decades based on
different observing techniques, as well as two analyses of historical data,
are commented. Most of them show also positive correlations between radius
variation and solar activity. With the noted exception of Calern, France, the
results obtained at other astrolabe stations during recent years are in
agreement with Santiago. The discrepancy between Calern and Santiago and its
probable cause are discussed.
Key words: astrometry / Sun: general
© ESO, 2004
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