# 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE SUN-LIKE ACTIVITY OF THE SOLAR TWIN 18 SCORPII

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