194 GETTING ACQUAINTED WITH THE STARS 



Wright Pierce 



This picture shows how the spectroscope is used. By means of this instrument 



the materials burned in the flame at the right are known by the patterns or bands 



they make in the spectrum of the instrument. 



indication of its becoming luminous is shown by a dull red 

 color, which, as it is heated longer, may change to orange 

 or yellow. If it is placed in a very hot furnace, it finally 

 becomes " white hot" and gives a brilliant whitish light. 

 Evidently, then, the color of a luminous body differs 

 with its temperature. This experiment gives us some 

 evidence on the temperature of stars. Our sun is believed 

 to have a surface temperature of about 11,000 F., and 

 gives a yellowish light. Some stars have exactly the 

 same color as the sun, and when seen through an instru- 

 ment called the spectroscope, they have the same spectrum 

 as the sun and so are believed to have about the same 

 temperature as the sun. Betelgeuse is a red star and 

 hence is not as hot as our sun, while Sirius, the Dog Star, 

 shines with a bluish-white light which indicates that it is 

 hotter than the sun. Half of the stars are white, while 

 most of the others are yellow. Some bodies that were 



