6 EXPERIMENTAL GENERAL SCIENCE 



which seems so brilliant, is probably only an insignificant 

 member of the universe, and if viewed from the nearest star, 

 would seem like a mere dot in the sky, if it could be distin- 

 guished at all. The difference in brightness which exists 

 among the stars affords one convenient means of distinguishing 

 them. The brightest are said to be stars of the first magni- 

 tude, the next brightest, of the second magnitude, and so on up 

 to the sixteenth magnitude. There are less than twenty-five 

 stars of the first magnitude. All the more conspicuous stars 

 have names of their own, as befits their importance; others are 

 given letters with reference to star groups. Some of these 

 larger stars are well known because of their frequent mention 

 in literature. Among these are Arcturus, Aldeboran, Polaris, 

 Lyra, Algol, Rigel, Capella and Vega. 



8. Light of the Stars. All the visible stars are hot bodies 

 like our sun, and shine by their own light. There is some 

 difference in the quality of the light, as may easily be seen by 

 comparing the brighter stars. Some have a bluish-white light, 

 while others incline to a reddish hue. There is reason for 

 believing that this difference in color indicates a difference in 

 temperature, and that the blue stars are much hotter than the 

 others. There are also large numbers of suns or stars that 

 seem to have cooled off so much that they no longer give light, 

 and it is possible that these dark stars greatly outnumber the 

 bright ones. Our own sun, like the others, is believed to be 

 cooling off, and in time may cease to send us light and heat. 

 This event is so far distant, however, that millions of years 

 must elapse before it occurs. The light that comes to us from 

 the stars moves at the rate of about 186,000 miles a second, but 

 even at that speed, the time required for the light of some stars 

 to reach us must be measured in hundreds or thousands of 

 years. The Pole Star (Polaris) is one of oifr nearest neighbors 

 in space, but it requires forty-five years for a ray of light to 

 travel from it to us. 



