CHAPTER II 

 TEMPERATURE CHANGES AND THE SEASONS 



15. Seasonal changes of temperature. The change of tem- 

 perature that comes with the seasons is to many of us the most 

 notable and striking difference between the seasons. Why 

 should there be such a difference? The sun still shines as 

 brightly as ever, and its heat has not decreased in the winter. 

 We are no farther away from the sun. Why are not our homes 

 warmed as well by the sun in winter as in summer ? In dis- 

 cussing this question it will be supposed that the reader remem- 

 bers from his study of geography the main elementary facts 

 about the sun and the earth. In any event it would be well 

 to review the subject of the earth's orbit, its revolution and 

 rotation, and its inclination upon its axis. 



16. Relation of the seasons to the sun. All apparent changes 

 in the sun's position are due to the movement of the earth 

 around the sun, and to the inclination of the earth's axis 

 (fig. 14). We often say that the sun rises and sets, when 

 we know that these appearances are due to the motion of the 

 earth. In the same way we say that the sun is higher in 

 the heavens in summer than in winter, meaning that we have 

 changed our position so that the sun appears higher. It is also 

 noted that daylight lasts longer in summer than in winter. 



We therefore know that as the seasons change there is also 

 a change in the apparent altitude of the sun and in the length 

 of day and night. It is to these changes that the seasons are 

 due. 



17. Effects of changes in sun's altitude. Why should it 

 make any difference in the heat that we get whether the sun 

 is high up in the heavens or lower down near the horizon ? 



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