All of the stars you can see with your own eyes are orbiting the vast swirl of hundreds of billions of stars we call the Milky Way Galaxy. But
our lives are so short in cosmic terms that we cannot easily sense their movement across the sky. Again, we need to be a bit clever with
our measurements. Stars actually do drift through space. The angular distance that a star will seem to move through space in a given
year is typically very, very small; virtually immeasurable. It tends to be smaller than the size of a star image on a photographic plate. This
annual motion due to the flight of the star through space is called proper motion. Barnard’s star has the highest proper motion and that is
only about ten arc seconds per year. Because of the proper motion of its constituent stars, the Big Dipper has not always looked the same
in our skies.
But a star’s apparent motion through space is sometimes an illusion as well. Because of our orbital motion, we see an effect called
annual parallax. This parallactic shift is used in stellar distance determinations.