Carolynn Server, age 11, of Rochester, New York, for her question:

How fast does the earth rotate at any given point?

Let's start from what we know of the general picture. In 24 hours, minus about four minutes, the earth rotates once around its axis, the fine line that runs from pole to pole straight through the center. The whole globe spins around as one single unit. This rotation speed as a total unit varies very little. However, the Big Ball bulges at the equator and the surface curves toward the poles, which are the opposite ends of the axis. Hence, the bulging waistline has to rotate much faster to keep up with the rest of the spinning surface.

The lines of latitude and longitude can give you a rough idea of the rotation speed at any point on the world map. Just remember that any point of the same latitude rotates around at the same speed. How fast it goes can be figured from the distances between longitudes. For example, in 24 hours, the entire globe rotates once around a circle of 360 degrees.

These degrees match the half circle meridians that mark the 360 degrees of longitude, the north south lines that run from pole to pole to pole. Every hour the longitudes rotate 15 degrees, which is 1/24th of a complete circle. Hence, the mileage between 15 degrees of longitude gives the speed of surface rotation. However, the longitudes taper to meet at the poles. As the distance between them decreases, so does the rotation speed.

At the equator, the longitude degrees are almost 70 miles apart and rotation speed is 1,050 miles per hour, Where the longitudes meet and pinpoint the poles, rotation is at a stand still. Lines of latitude help us to grade the distances between the longitudes at various points. Every spot on each circle of latitude rotates at the same speed. And everywhere the key to miles per hour is the distance between 15 degrees of longitude.

The distance from the equator to the North or South Pole is about 6,000 miles. It is sectioned by 90 latitudes, hence, a third of the distance is 30 degrees of latitude. Two thirds is 60 degrees. If sae divide the equator's rotation speed by three, we get a rough idea of the rate at which rotation decreases farther north and south. That is, if the globe were a perfect sphere. At Latitudes 30 degrees North and South, surface rotation should be about 700 miles per hour. At Latitudes 60 degrees, this should decrease to 350 m.p.h.

These samples give a general idea of how, why and where rotation speeds would vary on the surface of a picture perfect globe, however, our dear old globe bulges here and there, causing irregularities in the placement of its latitudes and longitudes. Experts have allowed for these oddities and measured our samples in more precise metric figures. They give the equator's rotation speed as 469 meters per second, which is fairly close to our mileage. But the latitude 30 circle rotates at 403 and latitude 60 at 233 meters per second. What's more, satellites and other new devices may refine even these careful measurements.