January 13: Olin Chaddock Wilson

Mt. Wilson Observatory, 100-inch Hooker Telescope

Olin Chaddock Wilson (January 13, 1909 – July 13, 1994) was an American astronomer best known for his work as a stellar spectroscopist. He studied astronomy and physics at the University of California, Berkeley and wrote his first scientific paper in 1932 on the subject of the speed of light. He received his PhD from the California Institute of Technology in 1934.

Wilson was a staff member of Mount Wilson Observatory for most of his research career where he studied stellar chromospheres. He was the first scientist to discover activity cycles, similar to the solar 11-year sunspot cycle, in other stars. 

In collaboration with Vainu Bappu he also showed that there was a correlation between the width of the Ca II lines in stellar spectra and the star's luminosity, the Wilson-Bappu Effect. The widths and shapes of the spectral lines told them about stellar rotation and atmospheric turbulence. The presence of sharp non-stellar absorption lines in the spectra told them about the amounts, temperatures, and random motions in the foreground interstellar matter. The presence of emission lines told them about chromospheric matter and excited matter around the stars.