THE SUN AND OTHEE STARS 269 



our earth. In light-giving power some stars are 100 times, 

 some 1000 times, and some even 10,000 times as great as our 

 sun. Our sun would be invisible without telescopic aid if it 

 were as remote from us as are most of the stars which we see. 



The sun gives us more light and heat in a second of time 

 than all the stars together do in fifty years. Since, in many 

 cases, they are larger than our sun, they must be exceedingly 

 remote. The nearest one which can be seen from the United 

 States is 5,000,000 times as far away as we are from the sun. 

 It is so far away that eight years are required for its light 

 to come to us at the rate of 186,000 miles per second. Since 

 most of the stars we see on a clear evening are many times 

 this distance, we are made to feel almost helpless in our effort 

 to understand the meaning of space. Some stars are so far 

 away that light reaches us a thousand years after it is radi- 

 ated, and the telescope shows stars which require many 

 thousands of years for their light to reach us. 



273. Stars of different magnitude. The 20 brightest stars 

 are taken together and are called stars of the first magnitude. 

 They are about two and one-half times as bright as the next 

 group, which are called stars of the second magnitude. Ex- 

 amples of the,se are the Pole Star and the stars in the Big 

 Dipper. In the whole sky there are 65 stars of the second 

 magnitude. Stars of the second magnitude are two and one- 

 half times brighter than those of the third, of which there 

 are 190. Similarly, the third magnitude is two and one-half 

 times brighter than the fourth, and so on. The faintest stars 

 which can be seen with the unaided eye are of the sixth 

 magnitude. There are in the first six magnitudes alto- 

 gether about 5000 stars, only half of which are above the 

 horizon at one time. Ordinarily one cannot see more than 

 2000 stars at one time on a clear evening. Under high 

 magnification, however, innumerable stars may be seen, and 

 sometimes these appear merely as great masses of nebulous 

 matter (fig. 132). 



