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Session 120 - The Sun.
Oral session, Saturday, January 10
International Ballroom East,
We have observed an apparent change in the solar radius that is in phase with the solar cycle during cycle 22. The maximum radius was during the period corresponding to the maximum of solar cycle 22. The data are from two full-disk photometric telescopes in daily operation at the San Fernando Observatory. Each telescope has a linear array of photodiodes and obtains a complete image of the sun by using the earth's rotation to scan the array from west to east across a solar image produced by an achromatic objective lens. Examining the radius for the red images (673 nm, bandpass 10 nm) we find that the radius exhibits a peak to peak variation of approximately 0.3 to 0.4 arc-sec. This result is in approximate agreement with that found by Ulrich and Bertelo (1995) from Mt. Wilson images obtained in the wing of the Fe-line 525.0 nm. However, our results refer to deeper layers in the photosphere since the SFO red images are very nearly continuum images. Whether this variation represents a real change in the solar radius or just a change in the structure of the atmosphere remains to be seen. This research has been partially supported by grants from NSF and NASA.
