When we leave the solar system, we come to the spaces between the stars. These distances are so vast that it is not easy to describe them as a certain number of millions of miles. Some idea of the distance of the nearest star can be gained by a comparison devised by Robert H. Baker of the University of Illinois: If the earth's path around the sun is represented by the circumference of a period on this page, then the nearest star would be a microscopic speck

Sirius, the brightest star in the heavens. It is in the constellation of Canis Major (the Large Dog) and is sometimes called the Dog Star. If a photographic plate is exposed long enough to record the faint stars, the bright stars are over-exposed. That is why Sirius occupies such a large space in this photograph.

200 feet away! We recall that the radius of the earth's path around the sun is nearly 100 million miles. If this distance is represented by a mere period on this page, then two hundred feet to the nearest star is a real distance. To represent these distances by reasonably small figures a much larger "yardstick" than mere miles must be employed.

We are all accustomed to changing our unit of measurement, our "yardstick." Very short distances are conveniently measured as so many sixteenths of inches. We say a neighbor's house is, perhaps, 150 yards away. We would not think of saying that our neighbor's house is 86,400 sixteenths of an inch distant. So as distances increase, we use larger "yardsticks." In this era of auto-mobiles, we sometimes say the next city is four hours distant by car. In that case we may assume that the car is going 40 miles an hour. If we wished, we might say that the city is four automobile hours distant. Astronomers have used a very similar device to represent, in small numbers, the distance of stars. An automobile, however, is altogether too slow for this purpose. The distances are so great that astronomers had to take the fastest thing they could find, which is light.

In ordinary experiences on this earth, light appears to be instantaneous; but when it has to travel between one star and another, it takes time and sometimes a great deal of time. By laboratory experiments it has been found that light travels at the rate of approximately 186,000 miles per second. Therefore, it takes light less than two seconds to go from the earth to the moon and about eight minutes to reach the earth from the sun. So, if the impossible happened and the sun suddenly became dark, we would not know it for eight minutes.

It would take too many figures to represent the number of minutes or even hours that it takes light to reach us from the nearest star. So we stretch our "yardstick" until it is as long as the distance light travels in one year, always traveling at the rate of 186,000 miles per second. This distance is called a light-year. The distance of the nearest star is a little more than four light-years.

Constellation of Taurus, or the Bull. His head is the cluster of stars in the center. The brightest star is Aldebaran. The small cluster in the right upper corner is the Pleiades.

We have so far found only two stars which are as near as about four light-years. Most stars are many times that distance. We have now moved into a different world, where interstellar spaces (spaces between the stars) are so great that it is almost impossible to comprehend them. But before we explore the stellar universe let us go back to the early Babylonians and the ancient Greeks, who named the constellations.

The stars which we see at night are scattered through space much like trees in a forest. There is this difference, that the trees are a few yards apart and the stars are a few light-years apart. By accident sometimes several stars may seem to be in a straight line. They look like little electric lights, all about the same distance from us. In reality they may differ tremendously. If there are three stars, which seem to be nearly in a straight line, the left-hand one may be twelve light-years away, the middle star thirty-two light-years, and the third star, perhaps, is the nearest of all, five light-years. It is obvious that if you could fly around among the stars, you would find no straight line at all.

When you walk through the woods or past rocky hills, you will occasionally see some rocks in the distance which look like a familiar object, perhaps the profile of a face. When you get near by, you may find that the rock which made the nose is a hundred feet beyond the small group of rocks that made the chin. This small group of chin-rocks may be scattered over a few yards of surface. It just so happened that rocks which weren't even near neighbors lay in such a way that at your distance they made a very good human profile.

Constellation Of Scorpio

The very bright star is Antares. The scorpion's tail is well indicated in the lower left corner.

The Constellation of Scorpio, One of the most beautiful constellations in the sky. Its principal star is Antares.

The Constellation Of Bootes

At the right is the handle of the Dipper; at the left, the Northern Crown. The brightest star is Arcturus.

Some stars, which have no connection whatever with one another, give the illusion of picturing such things as a dipper, lion, or scorpion. Such a group of stars is called a constellation. The ancient peoples were fond of these star groups because they used them as convenient parking places for their gods. Sometimes the constellations picture a very stirring scene. For example, there was supposed to be, in olden times, a very beautiful girl named Andromeda. She had been chained to a rock, and a fierce dragon prevented anyone from coming to her rescue. But Perseus, a Greek hero, after killing the terrible Medusa, who had snakes for hair and the power of turning any creature into stone, did come to the rescue of Andromeda. With the head of Medusa, which he had cut off and carried with him, he turned to stone the formidable dragon.

The next scene of the story is pictured in the sky. We see Andromeda chained to a cliff, with the dangerous dragon at her feet. Just to the north, a group of bright stars represents Perseus. He has a short sword in one hand and the snake-covered head of Medusa in the other. For reasons unknown, the Greeks never put the next act of this play in the sky. For more than 2,000 years astronomers have looked upon this exciting act and wondered what was going to happen next.

The star chart on page 164 shows another legendary Greek character - Bootes, the plowman, holding a crook in his right hand. Most constellations can be called just pure imagination. There are exceptions, of course. The Great Dipper in the northern sky does look like the very crude drawing of a dipper the kind of drawing a savage might make. It is really the tail and part of the body of the constellation called the Great Bear. Then there is in the southern part of the sky the constellation called the Scorpion. This is a fairly good outline drawing of a scorpion. Its principal star is the extremely bright and reddish star named Antares.