Gary Kubalak, age 14, of Superior, Wisconsin, for his question:

How fast does the earth move?

Our dizzy old planet spins, circles and boomerangs    all at different speeds in different directions. It also manages to crowd into its busy schedule a few nods and swerves. Most of its motions are fantastically fast but none of them maintain perfectly even speeds. What's more, its dizzy directions do not follow perfect geometric patterns. All these details are hard to verify and most of them are subject to revision at any time on the basis of new evidence.

The earth's largest and fastest sweep is a swing around the galaxy. This speed is computed in a roundabout way, based on the estimated distance of our solar system from the center of the starry pinwheel. Since the galactic center is hidden behind dark nebulae in the constellation Saggitarius, this estimate is based on tedious measurements of local stars, plus the mass and motions of the galaxy as a whole. Need¬less to say, these factors may be revised with more precise evidence. But we know for sure that the speed and scope of this galactic rotation are stupendous.

In the past decade, the earth's galactic speed has been estimated at various figures from 130 to 150 miles per second. At present, many astronomers take it to be about 540,000 miles per hour. The complete solar system rotates at this speed as it swings around within the galaxy, keeping all its rotating and revolving planets precisely in their places as it goes. The radius of this circular path is some 26,000 light years. Each galactic rotation is one cosmic year, equal to 200 million earth years, or there¬abouts.

So far as we know, the cosmic year does not affect earthly events. But the calendar year brings us the changing seasons. We travel this 600 million mile orbit around the sun in 365 1/4 days. The average orbital speed is 66,000 miles per hour. It is slightly faster in December, when we are closest to the sun and slightly slower in July when the distance between us and the sun is about three million miles longer. However, every calender day we travel more than 1 1/2 million miles with the earth as it orbits around the sun.

During that same period, we spin around from day to night as the earth rotates on its axis. Each rotation takes about four minutes less than the 24 hour calendar day. And the surface speed varies with latitude. At the equator, it rotates at 1,050 miles  per hour. From there it diminishes as we go north and south and gradually dwindles to zero at the poles. Recent evidence indicates that the earth's rotation is slowing down and each day is slightly longer than the previous one. If these figures are accurate, a century from now the average day may be about one second longer.

In addition to these three major motions, the earth performs at least five minor wobbles and weaves. These minor motions are too slight and too slow to be compared with the cosmic year, the calendar year or the daily rotation. True, we do not feel these fantastic speeds. This is because the variations in velocity are very, very slight. We feel the motion of speed only during rather fast accelerations and decelerations.