CHAPTER XXIII 



THE SEASONS AND THE SOLAR SYSTEM 



You have learned that a principal cause of what we call 

 the seasons is the variation, at different times of the 

 year, of the lengths of day and night. The longer the 

 day, the greater the heat, and vice versa. 



From this it appears to follow that the longest day of 

 the year should be the hottest day. Similarly, we noted 

 that it appears as though those points on the earth's sur- 

 face nearest the sun (mountain tops) would be the hottest. 

 But we found that other factors than nearness to the sun 

 affect this matter, and that, as a matter of fact, moun- 

 tain tops are cold. So as to the longest days. Other 

 factors than length of sunshine affect the matter, and 

 they are not the hottest days. 



June 21, as you probably know, is, in the northern 

 hemisphere, the longest day of the year, and yet most of 

 the heat of summer comes after that date. Similarly, 

 December 22 is the shortest day and, similarly, most of 

 the cold of winter comes after that date. Evidently, the 

 time of the greatest heat comes after the time of the great- 

 est heating and, similarly, the time of least heat comes 

 after the time of least heating. 



You learned that, for certain reasons, the polar regions 

 never become warm, although there may be a great deal of 

 sunshine there at certain seasons; in fact, these regions 

 have the longest days of all, since there, for months at a 

 time, the sun never sets. For similar reasons, the region in 

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