218 Trees, Stars, and Birds 



lights. There is also the same interval between the 

 times when the earth's magnetism has the strongest 

 effect on a compass needle. The connection be- 

 tween these facts and sun spots is not well understood. 

 The sun emits a little less heat at times' of sun-spot 

 maxima. 



Viewing the sun. The sun's light is so intense as to 

 hurt our eyes if we look at it without something to ob- 

 scure it, as a smoked glass. By holding a reading glass 

 at the right distance from a wall or a sheet of paper you 

 can throw upon the wall or paper an image of a candle, 

 a window, or other source of light. In like manner, a 

 large image of the sun may be thrown on a screen by 

 means of a telescope. This instrument contains lenses 

 similar to the reading glass. The image on the screen 

 may be viewed without danger to the eyes. Another 

 way to study the sun is by means of photographs. 

 Much of what astronomers knew about the sun, until 

 recent years, they learned by viewing it with telescopes 

 at times of eclipses, when only the edge could be seen. 

 Now they use many other instruments in studying it 

 and much has been learned which you would think we 

 could not possibly ever know in regard to a body that 

 is 93,000,000 miles away. 



The cause of day and night. The sun is hidden from 

 our view every night by the earth itself getting between 

 us and the sun ; yet it is always shining on the earth. If 

 we could travel fast enough, we could keep in the sun- 

 light all the time. 



In ancient times people had no knowledge of the dis- 

 tance of tHe sun from the earth or of its size. It seemed 



