Rusty M. Weiss, age 13, of Tucson, Arizona, for his question:

Do stars have gravity?

Gravity is a property of matter, all matter. It is a built in force. Every speck of matter in the universe has its rightful quota of gravity    be it a planet or a moon, a speck of dust or a starry sun. The quota of gravity is related to the mass of a material object. And its mass is the amount of matter packed into its volume. The gravity of our dense planet is six times greater than the gravity of the less massive moon. The sun is made of seething gases    but gases also are made of particles of matter. It is, of course, a star large enough to swallow our dense little planet more than a million times.

However, the starry sun is not hollow. The gases in its fiery heart are crowded and heavy. Altogether, it is more than 300,000 times more massive than the earth. Its surface gravity is 28 times greater than that of our planet. If it were possible for a 100 pound earth boy to stand on the sun, he would weigh 2,800 pounds    more than a ton. Our sun is a fairly average star. The gravity of certain other stars is less strong. The surface gravity of a little white dwarf star is surprisingly strong because it is packed with so much matter.