In broadcasting, rotation is the repeated airing of a limited playlist of songs on a radio station or satellite radio channel, or music videos on a TV network. They are usually in a different order each time. However, they are not completely shuffled, so as to avoid varying the time between any two consecutive plays of a given song by either too much or too little. When measuring airplay, the number of times a song is played is counted as spins.
Stations playing new music typically have a short rotation of around four hours, while stations playing "classics" may go as long as eight hours. College radio and indie radio stations sometimes have no particular rotation, only the music director's suggested lists for the disc jockeys, or are totally freeform radio. Broadcast automation systems handle a limited rotation quite well, in turn making voice tracking easy. Even if a live person is present, the automation system at commercial stations usually picks the music ahead of time out of the current rotation, thus the DJ becomes only an announcer.
Heavy rotation or power rotation is a list of songs that get the most airplay on a radio station. Songs in heavy rotation will be played many times in a 24-hour period. A reason for playing the same song more than once a day is that many listeners tune in expecting to hear their favorite song, and most listeners don't listen to the radio for extended periods of time. Prolonged listening to a station that places songs in heavy rotation can quickly become unpleasant; such stations are not well-suited for retail environments, where employees must listen for hours on end, and doing so can breed contempt for the music and create a hostile work environment.
A song placed in "lunar rotation" is one that is only played in off-peak hours, usually late at night. There can be various reasons for this, but such songs are usually not hits and are played because of the personal musical preference of the DJ or programmer, to avoid more stringent daypart-based regulations on music content or to fulfill a broadcasting obligation such as Canadian content quotas. (See also "beaver hour".)
Recurrent rotation refers to a group of songs still frequently aired on a contemporary hit radio station several months or even years after the initial debut. It is also used to describe core songs in other radio formats as well. Most charts have special rules to determine when a song has become recurrent, at which point they are removed from current charts (such as the Billboard Hot 100) and placed on special "recurrent charts". Recurrent charts tend to be more static, with fewer week-to-week changes in popularity than current charts.
The Billboard charts include these lists:
Songs that survive in recurrent rotation typically form the basis of radio formats as years advance. A hit song that is left out of recurrent rotation will eventually become known as a "forgotten 45", a name derived from the fact that singles used to be released on 45 RPM records.