Stars

   A star is a body of luminous gas, like the sun. But as stars are much farther away from the earth than the sun, they appear to be only small points of twinkling light. With the naked eye it is possible to see about 2,000 stars at any one time or place but with the most powerful telescope over 1,000 million stars are visible. Although light travels at 186,000 miles a second, the light from the stars takes many years to reach the earth.

   Stars are not fixed in space, but are travelling in different directions at different speeds. Seen from the earth, these movements appear to be so small that groups of stars, or constellations, seem to have a permanent relationship. The star patterns we see in the sky are almost the same as those seen by our ancestors hundreds, or even thousands of years ago.

   The sizes of stars vary tremendously, from about a tenth of the diameter of the sun to 20 times its diameter. Most stars appear to be white when looked at with the naked eye, but some are bluish-white, yellow, orange and red. The varied colours are due to differences in surface temperature. The brilliant, white stars are the hottest with temperatures of several hundred  thousand degrees. The less brilliant, orange and red stars have a temperature of about 2,000 degrees.

There are exceptions, however. The red giant, Betelgeux, in the constellation (or group) of Orion, appears to be brilliant because of its size. Its diameter is 250 million miles, which is greater than the diameter of the earth's orbit round the sun.

Shooting stars which are sometimes seen moving across the night sky for a few seconds are really meteors. These small particles flare up as they strike the earth's atmosphere but soon burn out.