Science for beginners . Fig. 170.—Slant of suns rays atlatitude 49° on June 21 and Decem-ber 22. Fig. 171.—Slant of suns raysat latitude 30° on June 21 andDecember 22. Therefore, at north boundary of the United States the sunleats the earths surface but about % as much at noon onDecember 22 as it does at noon on June 21. In the same way Fig. 171 shows how the heating power of THE SUN—THE CAUSE OF THE SEASONS 213 the sun varies at latitude 30°, approximately the south bound-ary of the United States. The altitude of the sun at noon,at 30° north latitude on June 21 is 83y2°, and at noon onDecembe
Science for beginners . Fig. 170.—Slant of suns rays atlatitude 49° on June 21 and Decem-ber 22. Fig. 171.—Slant of suns raysat latitude 30° on June 21 andDecember 22. Therefore, at north boundary of the United States the sunleats the earths surface but about % as much at noon onDecember 22 as it does at noon on June 21. In the same way Fig. 171 shows how the heating power of THE SUN—THE CAUSE OF THE SEASONS 213 the sun varies at latitude 30°, approximately the south bound-ary of the United States. The altitude of the sun at noon,at 30° north latitude on June 21 is 83y2°, and at noon onDecember 22, it is 36y2°. It is seen from the figure that thesuns rays spread over about 1% times as large an area ofearths surface in the winter solstice as at the summer these facts would you expect the greater difference intemperature between summer and winter in North Dakota orin Texas?. Fig. 172.—The length of day. 222. Length of Day and Its Effect upon the HeatingPower of the Sun.—The days and nights are always equalin length at the equator, 12 hours each. The poles of the earthhave six months day and six months night. Between theequator and the poles, the length of day and night is con-stantly changing. At latitude 40° north, the days vary inlength from about nine hours on December 22 to 15 hourson June 21. The farther north we go the longer the summerday becomes till we reach the north pole when the day issix months in length. Just why this is so is easily shownby experiment. Exercise -To Show Why the Length of Day Varies at DifferentPlaces on the Earths Surface (a) Use an orange or a small schoolroom globe for this experi-ment, and perform it in the evening or in a darkened room. Place 214 THE SEASONS—CLIMATE AND HEALTH a lighted lamp upon the table and hold the orange a few feet fromit. If you use an orange, let the stem and the bloom scars of theora
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