Constellations Are Not Constant. Stars that you see at night belong to the Milky Way galaxy. The sun sits on one of the galaxy's arms and rotates around the center of the galaxy. Other stars in the galaxy follow their own orbits as well. This stellar motion causes constellations to change their shapes over time, but it takes a long time for people to see those changes.
The constellations stay the same night after night. The patterns of the stars never change. However, each night the constellations move across the sky. They move because Earth is spinning on its axis.
