Definition of proper motion in English:

proper motion


mass nounAstronomy
  • The part of the apparent motion of a fixed star that is due to its actual movement in space relative to the sun.

    • ‘At perihelion, when proper motion reaches its maximum, it exceeds the diurnal motion, and the Sun turns slowly retrograde for a week.’
    • ‘Because the l = 1 dipole term is usually subtracted out from the data because it has large components due to our proper motion with respect to the cosmic background radiation.’
    • ‘In 1710, using Ptolemy's catalogue, Halley deduced that the stars must have small motions of their own and he was able to detected this proper motion in three stars.’
    • ‘His method of selecting a star was based on his own data for he chose the star which had the greatest proper motion of all the stars he had studied, correctly deducing that this would mean that the star was nearby.’
    • ‘His work on applying trigonometric methods to astronomical problems led him to note correctly that comets displayed a proper motion against the background stars.’