proper motion
  • Motion of a star or some other celestial object caused by its own movement rather than that of the Earth. Stars with large proper motions in the sky are certain to be comparatively close to the Earth. Barnard’s Star has the fastest proper motion of any star in the sky, but even this is only 10 arc seconds per year, so that it would take 180 years to travel the diameter of the full Moon in the sky.

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