Elizabeth Bacon, age 12, of Gary, Indiana, for her question:

What is celestial navigation?

Every young space alter can find the Big Dipper and use its pointer stars to locate Polaris. And every young space alter knows that Polaris is the Pole Star that points out the North Direction. This trick is one of the simple steps in celestial navigation. Celestial, of course, means the sky and everything is it, especially the stars. Navigation is the science of getting from place to place, especially over the trackless ocean. When a pilot plots his course by celestial navigation, he takes his bearings from the heavenly objects in the sky.

You can figure the east and west from the rising sun and the setting sun. A pilot may use these and dozens of other celestial guides to chart his way through the skies or across the ocean. He has charts and instruments to help him figure out his exact location from the data, part of which usually comes from his observations of sun, moon, stars and planets. What's more, the sky is the dial of a celestial clock from which he can tell the time.