What's a black hole? How old and how big is the universe? How many ordinary galaxies does it take to outshine a quasar? The Starchild Web site, developed by astrophysicist Laura Whitlock of NASA's Goddard Space Flight Center in Greenbelt, Md., provides colorful, illuminating answers to these and other astronomical riddles. Billed as a learning center for young astronomers, the site offers both elementary and advanced levels of explanation and exposition. Even adults may find this astronomical Web trek fascinating.