392] 



Our Earth and Its Fellow Planets 



That the sun stands still (aside from rotating on its axis) has 

 been known since the time of the astronomer Copernicus. Con- 

 sequently the earth must be moving, or we would have no change 

 from winter to summer or from day to night. The earth and all 

 the other planets travel around the sun and, at the same time, 

 turn, or spin, on an axis (the imaginary line that connects the 

 North Pole with the South Pole, in the case of the earth) . 



NIGHT AND DAY 



A good way to give a child a clear picture of some of the 

 causes and effects of the earth's motions is to have a lamp represent 

 the sun. An inexpensive globe may be bought at many five-and- 

 ten-cent stores, and as you rotate the globe and make it revolve 

 around the lamp, the youngster can see how light from the sun 

 varies at different parts of the earth. 



As the Earth Whirls Through Space: If we could stand out in 

 space to watch our earth, as we can observe the lamp and globe in 

 our room, we would see that the earth makes one complete turn 

 on its axis every twenty-four hours. This may seem very slow, but 

 at its widest part around the equator it is whirling at a rate of 



DAY CHANGES TO NIGHT AS THE EARTH TURNS ON ITS AXIS 

 As the earth rotates, some of it always faces the sun and has daylight. As rotation 

 continues, this portion is gradually turned away from the sun and night descends 

 there. All the planets rotate in this manner, and the length of a day on each 

 depends on the time it takes to make one complete turn on its axis. A day on Mars 

 is thirty-seven minutes longer than our twenty-four-hour day. Jupiter's day is 

 less than ten hours, while one day on Mercury equals eighty-eight of our days! 



