Patricia Belles, age 9, of Albany, N.Y., for her question:

How fast does the earth go around the sun?

The earth's orbit is about 186 million miles from side to side. In one year, it travels a distance of some 600 million miles as it makes one revolution around the sun. It travels at an average speed of 18.5 miles a second, but this orbital speed is a little faster in january than it is in July.

This is because the earth's orbit is slightly oval, and in january we are some three million miles closer to the sun. This part of the orbit is traveled a little faster. In july, when we are farthest from the sun, the earth travels a little slower. The differences are slight, and the average speed throughout the year is about 66,000 miles an hour.