A type of close binary star, typically containing solar-type and cool stars in which the light varies due to rotational modulation caused by starspots and chromospheric activity on the cooler component; abbr. RS. The light curve resembles a sine wave, but additional variations of up to 0.2 mag. with periods of years appear to be due to changes in activity akin to the solar cycle. These systems are officially classified as eruptive variable stars but should perhaps be included in the rotating variable star class. They are detached binaries, and many undergo eclipses as does RS Canum Venaticorum itself, which varies from mag. 7.9 to 9.1 every 4.8 days, with a secondary minimum of 8.2.