Antonia Jean Carroll, age 9, of Colorado Springs, Colo., for her question:

IF HEAT RISES, HOW IS THE EARTH HEATED BY THE SUN?

While it is true that heat rises, the heat we receive from the sun is actually in the form of radiation. The sun's heat radiates toward us. It's much like an electric heat lamp in your bathroom: it doesn't warm the air in the room but rather radiates heat directly on us.

The sun is so big that we don't have to worry about burning all of its heat supply. It has been glowing, scientists figure, for several thousand million years and will last even longer than that into the tuture. It's a big blazing ball: if you reduced the sun's size down to that of a basketball and the earth in the same proportion, the earth would be the size of a buckshot pellet.