Jenohn Lewis., age 13, of Omaha, Neb., for the question:

What is a galaxy?

A galaxy is a huge system of stars. It may also be called a Milky Way System a Spiral Nebula or an Island Universe. This last name gives a clue to its place in the heavens. For the galaxies are scattered throughout the vast reaches of empty space like blueberries in a muffin.

The Milky Way name gives another clue. The Milky Way we see in the night sky is a view across the huge galaxy in which we live. The Spiral Nebula name gives a clue to the shape of most galaxies. The billions of stars are often arranged like a spiraling pinwheel ‑ a crowded center with two or more spiraling arms.

The galaxy in which we live is a big one. It is shaped like a cartwheel, with stars clustered thickly in the hub and thinning out towards the rim. From side to side it measures some 100,000 light years. The hub in the center is some ten light years thick. Our sun is but one star among billions in our galaxy. Our galaxy is but one of millions scattered throughout the vastness of space.