Mae Lindner, age 13, of Birmingham, Ala., for her question:
WHAT IS THE MILKY WAY?
A glowing band of starlight coming from the billions of stars within our own galaxy or star system is called the Milky Way. At night we see it as a milky looking strip of stars because we are actually inside it.
Astronomers tell us that our galaxy is shaped like a pancake. The stars fan out from the center in many wide, curving arms that would give the galaxy a spiral or coil shape if we could see it from above.
During the winter, the Milky Way seems dimmer than it does during the summer. It crosses the sky near Orion and Cassiopeia. On a dark, clear summer night, it can be seen extending from the southern constellation Sagittarius, where it is brightest, to Cygnus, the great northern cross.
The Milky Way seems to have dark gaps in many places. These are formed by clouds of dust, called nebula, that block out light from the stars behind them.
The Milky Way contains clouds of dust and gas as well as planets, star clusters and stars.
Gravity holds the Milky Way together. All of its stars rotate around the center. But not all of the stars rotate with the same speed. Their speed depends on their position in relation to the mass or matter in the galaxy.
Stars such as our sun, which are far from the center, rotate around the center much as the planets rotate around the sun. They move this way because, for them, most of the mass lies toward the center.
Our sun moves in a circular path at a speed of 170 miles per second. Yet a complete trip around the center of the Milky Way takes the sun 200 million years. The stars slightly closer to the center move faster, because they are attracted with greater force.
The diameter of the galaxy is about 10 times greater than its thickness. It is so big that light, which travels 186,282 miles per second, takes about 100,000 years to travel from one end to the other.
Our solar system is a tiny speck located about 30,000 light years from the center of the galaxy. It is about midway between the upper and lower edges of the galaxy.
Light from the center of the galaxy cannot reach us through the dust, but scientists know from studying radio waves and infrared rays that there is intense activity there.
Astronomers have found that gas streams out from the center of the Milky Way at 1,000 miles per second, but they do not know why this happens.
Astronomers do not know how many galaxies there are. They have photographed millions of galaxies through telescopes and believe there are billions.
Many scientists believe that extremely bright, distant objects called quasars are galaxies. Some quasars may be more than 10 billion light years from earth.