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 d irectly correlated over an activity cycle. The ratio of the two correl ated changes shows considerable scatter. If we assume that the scatter represents variability of one solar-type star at different epochs, th e 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 w ith 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 t he Lockwood et al. 1992 sample) plus the Sun yields a possible increas e 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 198 0s. The limited sample of solar-type stars will need to be extended in order to improve the range of the estimate provided.