Proper motion is a term used in astronomy to describe the apparent motion of a celestial object across the sky. This motion is caused by the actual movement of the object through space relative to the Earth. Proper motion is usually measured in units of arcseconds per year and is an important factor in studying the dynamics and evolution of stars, galaxies, and other celestial bodies. By tracking the proper motion of objects over time, astronomers can gain valuable insight into their movement, origin, and future trajectories.