Beverly Young, age 11, of Rockford, Ill., for her question:
How do constellations form in the sky?
When you take a quick look, the glittering stars seem to be strewn carelessly all over the velvety dome of night. After you have feasted your eyes on their stupendous beauty for a while, you notice that they are arranged in odd shaped designs. These starry patterns are the constellations,
Your eye soon learns to recognize some of the constellations that adorn the starry night, one star design may remind you of a sprawling letter M. Ancient star gazers saw it as a seated lady and they named it for their queen Cassiopeia. Most of our constellations were named at the dawn of history, and some of the patterns are not quite what they were in ancient times. Gemini, the Heavenly Twins, has changed quite a bit in the past 2,000 years.
It is convenient to chart the stars as though they were all at the same distance and painted on the inside of a vast basin. Modern astronomers call this inverted bowl the celestial sphere, and they know that the stars really are at vastly different distances from us and from each other. All the stars in our skies, including the sun, are members of the gigantic Milky Way. Our round planet is surrounded on all sides by this auge pinwheeling system of stars. When we look up and out at the heavens we see familiar star neighbors in the Milky Way system.
Wren we look toward the east on a winter evening we see a section of the Milky Way that is occupied by a group of outstanding sparklers. Together they form an orderly design that rises and sets in orderly fashion with the seasons. This group is the constellation Orion. Its stars are far apart, and some are much nearer to us than others. They form a constellation because they are in the same general direction from the earth. Some of the stars of the Big Dipper are much nearer to us than others, but all the members of the constellation are in the same direction from us.
The Milky Way spins around like an enormous pinwheel, and every star in the sky is on the move. And they move at different speeds. Our sun and its planets rotate around the Milky Way galaxy at the fantastic speed of 170 miles a second. You would think that this motion would cause the stars to lose their places and that the constellations would change. And so they do, but these changes are slow because the spaces between them are so enormous. Through thousands of years there are slight changes in the constellations.
The stars occupy traffic lanes as they spin around the Milky Way. Some lanes travel faster and some slower than the lane occupied by the sun. Some overtake and pass us and others fall behind. This means that our starry neighbors are moving in different directions in relation to the Earth. All this motion gradually causes the stars to lose their places. In a million years, many of the constellations you see tonight will form different patterns in the sky above the Earth.