AEROGRAPHER'S MATE 3 & 2 



motions are of any importance to meteorology; 

 rotational motion, turning of the earth upon its 

 axis, and revolution around the sun, which 

 refers to the earth's orbit around the sun. 



In the first motion the earth rotates on its 

 axis once in 24 hours; one-half of the earth's 

 surface is therefore facing the sun at all times. 

 The side facing the sun is experiencing day- 

 light, and the side facing away from the sun 

 is experiencing darkness, accounting for our 

 day and night. Rotation about its axis takes 

 place in an eastward direction. Thus, the sun 

 rises in the east and sets in the west as 

 illustrated in figure 12-2. 



The second motion of the earth is its 

 revolution around the sun. The revolution around 

 the sun and the tilt of the earth on its axis 

 are responsible for our seasons. The earth 

 makes one complete revolution around the sun 

 in approximately 365 1/4 days. The earth's axis 

 is at an angle of 23 1/2° to its plane of rotation. 

 The earth's axis points in a nearly fixed 

 direction in space toward the North Star 

 (Polaris) at all times. 



Solstices and Equinoxes 



When the earth is in its summer solstice, 

 as shown for June in figure 12-3, the Northern 



Figure 12-2,— Rotation of the earth about its axis (during equinoxes). 



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