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Published February 1998 | public
Journal Article

Spatial dependence of solar-cycle changes in the sun's luminosity


We report observations of the large-scale spatial dependence of the Sun's luminosity variations over the period 1993–1995. The measurements were made using a new scanning disk solar photometer at Big Bear Solar Observatory, specially designed to measure large-scale brightness variations at the 10⁻⁴ level. Since the level of solar activity was very low for the entire observation period, the data show little solar cycle variation. However, the residual brightness signal ΔI/I (after subtracting the mean, first, and second harmonics) does show a strong dependence on heliocentric angle, peaking near the limb. This is as one would expect if the residual brightness signal (including the excess brightness coming from the active latitudes) were primarily facular in origin. Additional data over the next few years, covering the period from solar minimum to maximum, should unambiguously reveal the large-scale spatial structure of the solar cycle luminosity variations.

Additional Information

© 1998 Kluwer Academic Publishers. Received 21 January 1997; accepted 15 July 1997. This project was supported by the NSF and NASA.

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