William C. Pilcher, age 11, of Louisville, Georgia, for his question:

Can constellations change their shapes?

They can and they do. If we returned to the earth from several million years in the future, we would wonder what happened to the familiar constellations that now appear in our sky. Most of them would be twisted out of shape and some would be quite unrecognizable. A few observable changes have occurred in the past 2,000 years. For example, in Roman times Castor and Pollux were the twin stars of the constellation Gemini. Since then they have moved and now Castor is 1 1/2 times brighter than its twin.     

Such changes seem slow and slight because we see them across enormous distances. But actually all the stars are moving at fantastic speeds and changing their positions in relation to each other. The stars of the Big Dipper are moving in different directions. Because their distances are so remote, the changes are too slight to notice in a lifetime. But in 100,000 years, this constellation will be twisted into a different shape