El movimiento propio de una estrella es la medida del cambio de su posición en el cielo en el tiempo después de que se descarta el movimiento impropio. Es una medida indirecta de la velocidad transversal de la estrella con respecto a la Tierra. Esta contrasta con la velocidad radial, que es la medida del cambio de la distancia desde o hacia el espectador en el tiempo

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Proper motion is the astronomical measure of the observed changes in apparent positions of stars in the sky as seen from the center of mass of the Solar System compared to the imaginary fixed background of the more distant stars. The components of proper motion in the equatorial coordinate system (of a given epoch, usually J2000.0) are measured in seconds of time for right ascension (RA or α) and seconds of arc in declination (Dec. or δ). Their combined value is computed as the total proper motion (μ), which is expressed in seconds of arc per year (arcsec/yr) or per century (arcsec/100yr), where 3600 arcseconds equal one degree. Because most proper motions are much less than one arcsec per year, most modern catalogues, like the Hipparcos Index Catalogue (HIP), now express proper motion in terms of milliarcseconds per year (mas/yr), where 1000 mas equals one arcsecond. This transverse sky motion is separate from the radial velocity, being the velocity moving toward or away from the observer in kilometres per second (km/s), as obtained from the Doppler shifts in starlight seen with a spectroscope. Knowledge of the proper motion, distance, and radial velocity allow approximate calculations of a star's true motion in space in respect to the Sun. Proper motion is not entirely "proper" (that is, intrinsic to the star), because it includes a component due to the motion of the Solar System itself.

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