Anthony Ortiveros, age 10, of Santa Maria, California, for his question:

How many stars are there in our galaxy?

This is a very popular question but nobody can give the number exactly. Our galaxy is shaped like a big wheel with a thick center and streamers of starry arms spiraling out from the hub. Most of its teeming stars are crowded in the dense cen¬tral region and we are way out on a trailing limb. We have an edge way view across the Big Wheel. This is the view we see when we look up at the hazy Milky Way that arches across our sky. That milky haze is actually the blurred light from hundreds of millions of far away stars    and all of them belong in our own galaxy.

The Milky Way is blotched with dark clouds of cosmic dust and gas. These immense dark nebulae blot out our view of the stars behind them. They hide most of the stars around the crowded center of the galaxy. Astronomers, however, do not de¬pend entirely on what can and cannot be seen. They have other methods for figuring roughly the number of stars in our Big Wheel, and they estimate that the total number is about 100 billion. They also estimate that many of these teeming stars inay.have . planet systems somewhat like our own.