15. Patterns of stars in constellations hardly change in appearance over times of even a few thousand years. Why? A. Stars move, but they move very slowly-only a few kilometers in a thousand years. B. Although most stars move through the sky, the brightest stars do not, and these are the ones that trace the patterns we see in the constellations. C. The stars in our sky actually move rapidly relative to us-thousands of kilometers per hour-but are so far away that it takes a long time for this motion to make a noticeable change in the patterns in the sky. D. Stars within a constellation move together as a group, which tends to hide their actual motion and prevent the pattern from changing.
