The difference between the direction of a radiating source as it would be seen by a stationary observer at a specified point, and the direction in which the source is actually seen by a moving observer at that point. In the case of an observer on the Earth, stellar aberration has three principal components: diurnal aberration, resulting from the diurnal rotation of the Earth; annual aberration, resulting from the annual motion of the Earth about the Sun; and secular aberration, resulting from the motion of the Solar System's centre of mass.