Since the distance between the Zeeman sub-levels is a function of the magnetic field, this effect can be used to measure the magnetic field, e.g. that of the Sun and other stars or in laboratory plasmas.
Charley horse: Slang for a cramp in a muscle in the leg, usually caused by a strain or injury. A charley horse can last anywhere from a few seconds to over a quarter of an hour. It is not uncommon for one to recur before it finally resolves.
Charley horse is the common name for an involuntary muscle cramp, spasm, or contraction. Although the term usually refers to a nighttime muscle spasm in the back of your calf, it can occur in any muscle in your body.