FORM, MOTIONS, LATITUDE, AND LONGITUDE 207 



The motion of the earth through space during its revolution 

 about the sun is at the rate of about 600,000,000 miles a year. This 

 means that the earth travels about 1,600,000 miles daily, -66,666 

 miles hourly, or more than 1,100 miles each minute. 



The earth's axis is inclined toward the plane of its orbit about 

 23^ degrees (Fig. 202). This position of the axis, together with 



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Fig. 202. Diagram showing the position of the earth with reference to the 

 sun at the solstices and equinoxes. 



the motions of the earth, has much to do with the distribution of 

 the heat and light received from the sun, and so with the changes 

 in the length of day (daylight) and night, and with the seasons. 

 But before attempting to see how these changes are brought about, 

 we must become familiar with certain terms which are to be used 

 in the discussion of these changes. 



Latitude, Longitude, and Time 



Latitude. The equator has been defined as the circle about the 

 earth midway between the poles. Circles parallel to the equator 

 are parallels. The number of parallels which might be drawn is 

 very large, though only a few are represented on maps. The length 

 of parallels varies greatly, those near the equator being longer, 

 and those near the poles shorter. The lines that pass from pole to 



