The Probert Encyclopaedia of Science & Technology

ABERRATION

In optics an aberration is a defect in the image formed by a lens or curved mirror. In chromatic
aberration the image formed by a lens, but not a mirror, has coloured fringes as a result of the different extent to which light of different colours is refracted by glass. It is corrected by using an achromatic lens. In spherical aberration, the rays from the object come to a focus in slightly different positions as a result of the curvature of the lens or mirror. For a mirror receiving light strictly parallel with its axis, this can be corrected by using a parabolic surface rather than a spherical surface. Spherical aberration in lenses is minimized by making both surfaces contribute equally to the ray deviations, and can (though with reduced image brightness) be reduced by the use of diaphragms to let light pass only through the centre part of the lens. In astronomy an aberration is the apparent displacement in the position of a star as a result of the earth's motion round the sun. Light appears to come from a point that is slightly displaced in the direction of the earth's motion. The angular displacement a = v/c, where v is the earth's orbital velocity and c is the speed of light. Aberration was discovered in 1728 by the English astronomer James Bradley and was the first observational proof that the Earth orbits the Sun.

In astronomy, aberration is a small periodical change of the position in the stars and other heavenly bodies, due to the combined effect of the motion of light and the motion of the observer; this is called annual aberration, when the observer's motion is that of the earth in its orbit, and daily or diurnal aberration, when of the earth on its axis; amounting when greatest, in the former case, to 20.4', and in the latter, to 0.3'. Planetary aberration is that due to the motion of light and the motion of the planet relative to the earth. In optics, aberration is the convergence to different foci, by a lens or mirror, of rays of light emanating from one and the same point, or the deviation of such rays from a single focus; called spherical aberration, when due to the spherical form of the lens or mirror, such form giving different foci for central and marginal rays; and chromatic aberration, when due to different refrangibilities of the coloured rays of the spectrum, those of each colour having a distinct focus.
Research Aberration