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.