# 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE SUN-LIKE ACTIVITY OF THE SOLAR TWIN 18 SCORPII
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Abstract
We present the results of 10 yr of complementary spectroscopic and photometric observations of the solar twin 18 Scorpii. We show that over the course of its 7 yr chromospheric activity cycle, 18 Sco’s brightness varies in the same manner as the Sun’s and with a likely total brightness variation of 0.09%, similar to the 0.1 % decadal variation in the total solar irradiance. Key words: stars: activity — Sun: activit