The methylidyne radical (CH) was the first astromolecule conclusively to be identified. CH was detected via electronic transitions in both the interstellar medium and in comets. The interstellar reports included papers by Swings & Rosenfeld in 1937, followed by McKellar in 1940, and Adams in 1941. A radio detection by Rydbeck et al. followed in 1974. The initial cometary detections were reported by Nicolet in 1938 and Dufay in 1940.

April 2007 - A new study by Sheffer & Federman reports the identification of half a dozen lines for CH in the UV region.

The CH radical is very reactive. It can be produced in hydrocarbon combustion and can even attack the very stable N₂ molecule.