A i g ] Recognizing the Stars 



The spectroscope analyzes the light of the stars and reveals what 

 chemical elements go into their make-up. On the basis of this 

 analysis the spectroscope estimates the rate at which the stars are 

 moving, and the direction of their motion toward the earth or 

 away from it. 



The spectroscope does more it reveals the age of the stars 

 through their size, color, and composition. The younger ones are 

 giant size and are composed of thin gases that shine with a rosy 

 hue. An older star is more condensed and shines yellow. In the 

 next age cycle it would shine white and blue; after that it is really 

 an old star and begins to cool. 



Through all its stages a star condenses and contracts. After its 

 old age, a star shines white, then yellow, then red at last becoming 

 cold and dead. Although a new star and a very old one both shine 

 red, their age can be distinguished by their size: A giant red star 

 is young, a small red star is old. 



THE INTERFEROMETER AND OTHER AIDS 



Another invention that has proved of great value to astron- 

 omers is the interferometer, a remarkable instrument that can be 

 attached to a telescope to measure the size of certain stars. There 

 are still other instruments that help us to know the stars. Scientists 

 use these instruments to measure the intensity of light and heat 

 on these far-distant heavenly bodies. Whatever instrument is used, 

 mathematical techniques are the key to success. Geometry, trig- 

 onometry, and the calculations they involve, originated with the 

 measurement of land on the surface of the earth, but they ended 

 up by leading us to the stars. 



Spectacular Sights in the Skies 



THE MILKY WAY FORTY BILLION STARS 



On a clear night, in open country, even a child will be able 

 to find the Milky Way without having it pointed out to him the 

 band it forms in the sky actually does have a milky-white appear- 

 ance. This cloudy band of light is made up of an enormous number 

 of stars an estimated forty billion 1 one of which is our sun. Many 



