Margaret Poster, age 11, of Richmond, Virginia, for her question:

Is the earth's orbit perfect?

Heavenly bodies tend to favor spherical shapes and move in circles or spirals. However, fern if any of these neat geometric designs are perfect. For example, though all the planets orbit around the sun, none of them orbit in perfect circles. Venus has the roundest orbit, though even it is slightly oval. The earth's orbit is a trifle more oval, or elliptical.

If our yearly orbit around the sun were a ,perfect circle, the sun would remain in the exact center. Its distance from us would be about 93 million miles at all times. But our orbital path is not quite a perfect circle and the sun is not quite at its exact center. In December, we are about three million miles closer to the sun than we are in July. This makes the earth travel a little faster in December than it does in July. It's orbit is not a perfect circle and, what's more, it does not maintain a perfectly uniform orbital speed throughout tile year.