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1. Spinning motion of a celestial body or a group of gravitationally bound bodies, such as a galaxy, about an axis, as distinct from orbital revolution. Almost all celestial bodies show some degree of rotation. Young stars arrive on the main sequence with a high rotation rate; this results from the conservation of angular momentum during their collapse from a cloud of interstellar gas. As a star ages, structural changes in its interior and interactions with its surroundings produce changes in its speed of rotation. The hottest (O and B) stars have very great rotation rates of about 200–250 km s–1. Sunlike stars spin more slowly as they age, although some are able to retain their rapid rotation. The faster the rate of rotation the broader and shallower the star's spectral lines and the stronger the magnetic field (see corona). See also differential rotation; direct motion; synchronous rotation.
2. One complete turn of a celestial body about its axis. The Earth takes one sidereal day to make one rotation. Ideally the rotation period of other bodies is measured as the time interval between successive passages of a meridian line on the surface across the center of the disk, as seen from Earth. The solid surface may however be unobservable and indirect measurements, as by radar, are then employed. The rotation period of a gaseous body, such as the Sun or the planet Jupiter, varies with latitude, being greatest at the equator (see differential rotation).
An operation performed on data in a register of the central processing unit, in which all the bits in the register are shifted one position to the right or left, and the endmost bit, which is shifted out of the register, is carried around to the position at the opposite end of the register.
Also known as rotational motion.
Motion of a rigid body in which either one point is fixed, or all the points on a straight line are fixed.
Angular displacement of a rigid body.
The motion of a particle about a fixed point.