Variations in the Solar Constant Caused by Changes in the Active Features on the Sun

Abstract

The solar constant is calculated as a function of time using known contrast values for active features on the Sun. The photospheric effective temperature is assumed to be constant in this model and the change in radiant output is assumed to be caused solely by active features on the Sun which have different effective temperatures than the surrounding photosphere. The theoretical annual mean solar constant varies by no more than 0.102 mW cm⁻² or 0.075% of its value. For the more active Sun the solar constant is lower. If the energy flux from the deep interior of the Sun is constant on the time scale of a century, the decreased radiant output at sunspot maximum may be balanced by energy storage in the active features or by increased convective energy. A compensating change in the photospheric effective temperature of 1.1°K at sunspot maximum is also sufficient to give a constant solar radiant output.