aberration of light
In astronomy, the apparent displacement in position of a heavenly body caused by the combination of the velocity of light and that of an observer on the surface of the earth. Aberration of light due to the rotation of the earth on its axis is termed diurnal aberration. That due to the revolution of the earth around the sun is termed annual aberration. In optics, failure of an optical system to bring all light rays received from a point object to a single image point or to a prescribed geometric position. Spherical aberration is caused by rays from various zones of a lens or mirror coming to focus at different distances from the lens or mirror. Chromatic aberration (or chromatism) is due to the differences in refraction of the coloured rays of the spectrum; those of each colour having a different focus.