Brenda Dodge, age 11, of Coventry, R.I., for her question:

Can the sun pull down the earth?

The sun's mighty gravity tries hard to pull us down into its fiery furnace. But the earth has a way to escape. It refuses to fall down in a straight line. Instead it falls in a curved line. After about 600 million miles, this curved path leads us back to almost where we started. This circle is the earth's orbit. lie cannot fall into the sun as long as the earth keeps on whizzing around and around its orbit. And the earth can keep orbiting the sun forever and a day.

Our orbit is about 93,000,000 miles from the sun, which is a nice comfortable dis¬tance. To stay there, the earth must travel at a certain speed. It whizzes around its curved path at about 66,000 miles an hour. This is very fast, but we take a whole year to make one swing around our orbit. The sun cannot pull us straight down because we keep swinging around and around in circles.