The Surface Temperature of the Sun and Changes in the Solar Constant

The solar distortion telescope has been used to measure the limb shape and latitude dependence of the limb brightness during the summer months for a 5-year period—a time base sufficient to detect solar cycle trends in the data. Comparison of these observations with spaceborne measurements of the solar constant suggests that a significant part of the solar cycle variation in irradiance is a result of temporal changes in the latitude-dependent surface temperature of the sun.