Steve Cokes, age 13, of Glenpool, Oklahoma, for his question:

Why don't galaxies break apart?

First a message to pen pals who live out in the glorious countryside. Andy wonders whether a simple address will be certain to find you. For that reason he selects readers who add a box number or some other detail to direct the postman. Also, if you live in a small friendly community, naturally everybody there knows you and where you live. But Andy needs a more detailed address than just the name of your town.

Now to the question about galaxies. Even they have been given numbers, names and celestial addresses so that astronomers know where to locate them. The same astronomers tell us that these stupendous masses of stars and gases are made of matter. And all matter has its built in quota of gravity. A galaxy is held together by the combined gravity in its massive materials. This same mighty force also molds its shape and directs its motions.