470 



GENERAL SCIENCE 



FIG. 359. The position of the earth at the 

 equinox. 



" shooting stars. " They are small solid bodies, sometimes so small 



as to weigh only a fraction of an ounce. They are moving at a 



tremendous rate of speed, which causes a great deal of friction when 



they come within the atmosphere of the earth. They then become 



very hot and usually burn up, 

 just as a rifle bullet in passing 

 through the air gets very hot. 

 Sometimes, however, they are 

 very large, and when they fall 

 to the earth they are found 

 to weigh tons. They may 

 be small bodies which are in 

 space and are drawn toward 

 the earth by the power of 

 gravitation. Some scientists 

 have accounted for them as 



having been shot out by the sun or thrown into space by volcanoes 



on the surface of the moon. 



The small meteors or shooting stars are supposed to be tiny 



pieces of matter which once belonged to a comet. As the earth 



travels on through space it 



sometimes crosses the path 



where there are pieces of an 



old worn-out comet. At such 



times a great many shooting 



stars are seen in the heavens. 



Hundreds of these pieces 



are entering our atmosphere 



and are burned up before 



they reach the earth. Until FlQ . 360 . Position of earth at summer 



a meteor gets within about solstice. 



160,000 miles of the earth, 



it is attracted by the sun more than by the earth. 



Origin of the Solar System. It is believed that millions of years 



ago all the bodies we know about in the solar system existed as 



one great cloud called a Nebula. This enormous cloud of heated 



vapor began to cool and, growing smaller, took on a rotary or spin- 



