周年光行差

Aberration \Ab`er*ra"tion\, n. [L. aberratio: cf. F. aberration.
See {Aberrate}.]
1. The act of wandering; deviation, especially from truth or
moral rectitude, from the natural state, or from a type.
``The aberration of youth.'' --Hall. ``Aberrations from
theory.'' --Burke.

2. A partial alienation of reason. ``Occasional aberrations
of intellect.'' --Lingard.

Whims, which at first are the aberrations of a
single brain, pass with heat into epidemic form.
--I. Taylor.

3. (Astron.) A small periodical change of position in the
stars and other heavenly bodies, due to the combined
effect of the motion of light and the motion of the
observer; 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.

4. (Opt.) 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
colored rays of the spectrum, those of each color having a
distinct focus.

5. (Physiol.) The passage of blood or other fluid into parts
not appropriate for it.

6. (Law) The producing of an unintended effect by the
glancing of an instrument, as when a shot intended for A
glances and strikes B.

Syn: Insanity; lunacy; madness; derangement; alienation;
mania; dementia; hallucination; illusion; delusion. See
{Insanity}.