Dale Bittler, age 13, of Youngstown, Ohio, for his question:

How fast does the earth revolve around the sun?

In the last hour, the earth traveled about 66,600 miles along its orbital path around the sun. Naturally, you and every other earthling went along with it. The distance around the orbit is about 595 million miles    and one revolution is completed in 365 days, six hours, nine minutes and 9.54 seconds. This period of time is called the sidereal year    which differs from the solar year on which we base our calendar.

Actually the orbital speed varies very slightly throughout the year. This is because the earth's orbit is not a perfect circle. It speeds up slightly when it swings a little closer to the sun, which is in December. In July, we are three million miles farther from the sun and the orbital speed is a little slower. Taking these minuscule variations into account, the average speed at which the earth revolves around the sun is estimated to be 18 1/2 miles per second.