The expression “fixed in the stars” implies that celestial bodies are stuck motionless in the sky. But as a new short film created by the American Museum of Natural History explains, stars actually move. So why, then, do constellations like the Big Dipper appear to have remained in the same swath of sky for millennia, even though their luminous components all orbit the Milky Way's center at different speeds?

Learn the science behind the Big Dipper's position below, and see how the star group looked 32,000 years ago—and how it will likely appear in 50,000 years.

[h/t The Kid Should See This]