A METHOD OF DETERMINING POSSIBLE BRIGHTNESS VARIATIONS OF THE SUN IN PAST CENTURIES FROM OBSERVATIONS OF SOLAR-TYPE STARS

Observations of the Sun and a number of stars with mass and age close to the Sun show that changes in magnetic activity and brightness are directly correlated over an activity cycle. The ratio of the two correlated changes shows considerable scatter. If we assume that the scatter represents variability of one solar-type star at different epochs, the aggregate data may represent the range of variation of the Sun over centuries. We illustrate a technique of inferring possible brightness variations of the Sun from a sample of solar-type stars. The observed scatter of the ratio of all 10 solar-type stars in our sample (stars with 0.55 less than or similar (B-Y) less than or similar 1.2 and mean level of chromospheric activity R(HK)' less than or similar -4.75 in the Lockwood et al. 1992 sample) plus the Sun yields a possible increase of 0.2%-0.6% in solar brightness as magnetic activity has increased from the Maunder Minimum (ca. A.D. 1660-1710) to the decade of the 1980s. The limited sample of solar-type stars will need to be extended in order to improve the range of the estimate provided.