Radius of the Sun in relation to solar activity

Abstract

Radius of the Sun has been measured by many researchers using various techniques over more than three centuries, which demonstrated that the solar radius is not constant in time, but exhibits significant variations. As in cases of variations in most other observed features of the Sun, correlation has been saught between solar radius and sunspot numbers, the latter being recognized as the best index of solar activity. However, such studies have so far produced completely contradictory results, viz., both correlation and anticorrelation have been reported. The reason appears to be the data used, which is highly inhomogeneous. I report here a statistically significant relationship between solar radius and sunspot numbers in the sense that a larger diameter of the Sun is associated with higher levels of solar activity, when a homogenised data base covering observations over the last three centuries is used for solar radius.