proper motion

The slow motion of a celestial object across the sky, relative to other objects, due to the actual velocity of the object, for example, in its orbit around the center of the galaxy. While all celestial objects appear to move across the sky from hour to hour because of the rotation of the Earth, a few stars shift their position relative to the others when observed year after year. This relative shift in their position is their proper motion. Stars that exhibit proper motion tend to be relatively nearby and are whizzing through the solar neighborhood. Even though they are moving at many thousands of miles per hour (hundreds of km/s) relative to us, they are still far enough away that they only appear to move a few arc seconds per year or less.