HOW FAR AWAY ARE THE STARS? 189 



others. Some of the better informed men became astrol- 

 ogers. These men believed that the stars exercised magic 

 influence over people, and that such people must do the 

 things that the stars ordered them to do. Even today 

 we see ignorant people believing in the predictions of 

 fortune tellers who say that they live under a lucky or an 

 unlucky star. Some of our superstitions of today have 

 been handed down from very ancient times. 



But the early astrologers knew a great deal about some 

 of the stars. They could tell several planets and gave 

 them names. The name " planet" itself comes from the 

 Greek word meaning to wander, for they saw that these 

 heavenly bodies moved about. The old astronomers 

 could predict with a good deal of accuracy the movement 

 of some stars, although they did not know what caused 

 them to be seen in different positions in the sky. The 

 old idea was that the earth was fixed, and it was not until 

 the 16th century that Copernicus, 1 a Polish clergyman, 

 proved that a number of planets were revolving in space 

 around the sun. He believed our own earth was one of 

 these and that the earth rotated on its axis, making it 

 appear as if the stars moved about the earth. In the 

 units that follow, we shall build on the experiences we 

 have had in our geography and try to get a little more 

 knowledge about some of our neighbors in space. 



PROBLEM I. HOW FAR AWAY ARE THE STARS? 



When we look up into the sky, we may think that we 

 see myriads of stars, but if we try to count them, we are 

 surprised to find that we rarely see more than 2000 or 

 3000 at one time. If we were to look through a big tele- 

 scope, such as they have at the Mount Wilson Observatory 

 in California, we could see thousands of stars where we 

 saw only one with the naked eye. This is so because the 



1 Copernicus (ko-pur'ni-kws). 



