Christina Lancaster, age 11, of Ottawa, Ontario, Canada, for her question:
HOW MANY STARS ARE IN THE SKY?
A star is a huge ball of glowing gas in the sky. Our sun is a star and it is the only star close enough to earth to look like a ball. Most others are so far away that they look like pinpoints of light, or else we can't see them at all without a telescope.
No one knows just how many stars are in the sky. On.a clear night, however, we can see about 2,000 which is only half of the sky. On the opposite side of the earth a person could see another 2,000, giving a total of about 4,000 that can be seen without a telescope.
If you use a telescope with a lens that is three inches in diameter, you would be able to see another 600,000 stars. By using an even larger telescope it is possible to see about 3 billion individual stars and more than 1 billion galaxies.
If you were to combine all of the stars in all of the galaxies, you would have more than 200 billion billion stars. Here's how that number looks printed out it is the number two followed by 20 zeros: 200,000,000,000,000,000,000.
Very few stars have names. Who could come up with 200 billion billion different names? Only the brightest are given names, such as Rigel and Betelgeuse in the constellation Orion. To identify a star today, astronomers use a letter of the Greek alphabet with the name of a constellation.
The sun is about 93 million miles from earth. The star nearest the sun is called Proxima Centauri, and it is about 25 million million miles from the earth. Astronomers measure the distances between the stars in units called light years, and they say that Proxima Centauri is 4.3 light years away.
A light year equals 5.88 million million miles. This is the distance light travels in one year at a speed of 186,282 miles per second. Some stars are as far as 80,000 light years from earth.
The earliest recorded astronomical observations were made in China about 3000 B.C. A Greek astronomer named Hipparchus was the first to draw up a catalog of stars that showed their brightness and position. He did his work about 100 B.C.
In 150 A.D., an astronomer in Egypt named Ptolemy cataloged more than 1,000 stars and proved wrong the ancient idea that no change in the heavens could occur.