New light on sunspot darkness and the solar cycle

Abstract

NUMEROUS attempts have been made to find the physical mechanism responsible for the sunspot cycle. Present theoretical discussions of the basic mechanism of solar activity are usually based on a dynamo theory with a reversing magnetic field1, but objections and alternative interpretations1,2 have recently been advanced. Our understanding of the sunspot cycle seems to be in a stage where new observational insight may be valuable. We report here a variation in the infrared umbra intensity of large sunspots with the phase in the solar cycle.