Starting in the 1960's at the Mt. Wilson Observatory O.C. Wilson (sic) began a long - term study of magnetic cycles in cool stars using as his observational indicator the variable emission flux of the H and K resonance lines of ionized calcium whose appearance in emission is characteristic of stellar chromospheres. (stsci.edu)
The 22 - year magnetic cycle was discovered in 1925 by the American astronomer George Ellery Hale. (britannica.com)
Understanding this cycle is one of the biggest outstanding problems in solar physics, in part because it does not appear to match magnetic cycles observed on other solar - type stars — leading some to suggest the Sun is fundamentally different. (sciencedaily.com)