Carlene Wells, age 11, of Florence, South Carolina, for her question:

What exactly are galaxies?

A galaxy is a huge family of perhaps more than a hundred billion stars. As a rule it is shaped like a super sized cart wheel. Most of the stars are crowded together in the center. Other stars stream outward from the center in long spiraling arms. This sort of star system is called a spiral galaxy. And all its stars turn around and around    somewhat like a stupendous pinwheel.

In the vast reaches of space, there are thousands and thousands of galaxies. And one of them is our own home in the heavens. Our sun is just one of its 100 billion stars. Our Solar System is just a tiny part of it, far from its crowded center. Traveling at the speed of light, it would take a hundred thousand years to cross our galaxy from side to side. From our position we have an edgewise view across it. What we see looks like a pale glimmering arch over the sky  ¬and we call it the Milky Way.