Steve Nelsen, age 10, of Des Moines, Iowa, for his question:

What is a stationary satellite?

Satellite tracking is great dun. If you scan the skies long enough with even a small telescope, you are bound to spot at least one. The bright eyed little traveler moves faster than its background of stars. And, chances are, it moves towards the east. The earth below it also is moving eastward. The spot on which you stand rotates clear around the globe every 24 hours. If you stand on the equator, your spot rotates at about 1,000 miles an hour. Farther north and south, the rotation speed is slower. While a satellite orbits the earth, the ground below it rotates around the earth's axis. Both may move eastward, but if the satellite moves across the sky, they are moving at different speeds.

If the satellite is faster, it will race ahead of your spot below it and appear to pass eastward across the sky. If the satellite were slower than the earth's rotation, it would lag behind and seem to pass westward. But suppose the two speeds were exactly matched. The satellite orbiting at about 22,000 miles above the equator and the spot below it would move around at the same rate of 1000 miles per hour.  It would stay above the same spot as a stationary satellite. Satellites of this kind are used for communication systems. Fixed at certain distances, they are be able to relay radio, telephone and TV signals around the globe.