differential rotation

The rotation of a gaseous body, such as the Sun or the planet Jupiter, at a rate that varies with latitude, or the rotation of a non-solid, disc-shaped structure, such as a galaxy, at a rate that varies with distance from the centre. A solid planet like the Earth must rotate so that the angular velocity is the same everywhere. However, the equatorial regions of a gaseous planet or star rotate more quickly than regions at higher latitudes, so two features at differing latitudes will move relative to each other. In a galaxy, the component parts (stars and clouds of interstellar material) are in individual orbits around the centre of the galaxy. The angular velocity varies with radial distance from the centre, so the galaxy does not rotate like a solid disc.