Our Earth and Its Fellow Planets [ 393 



more than a thousand miles an hour! At places north and south 

 of the equator the rate is not quite so fast. The rotating speed at 

 San Francisco, Chicago, and New York is 750 miles an hour. 



Sunrise, Noon, and Night: Just as our lamp illumines only half 

 the globe at a time, so the light of the sun shines on only half the 

 earth at a time. This is what gives us our alternation of night and 

 day. As the earth turns so that we can see the sun from our particu- 

 lar spot on earth, we say that "the sun is rising." 



The earth continues to turn eastward and the sun appears to 

 rise higher and higher in the sky. When the sun is as high as it 

 "can go," we have "noon." After that the sun seems to sink lower 

 and lower until the earth has turned so far that we can no longer 

 see the sun from our particular spot on earth. We say that "the 

 sun has set." It is now night on our side of the earth but on the 

 other side of the earth, day is beginning. 



Why the Amount of Daylight Varies: The path that the sun 

 appears to follow in the sky varies according to our location on 

 the earth. If we were at the equator, we would find night and day 

 of equal length throughout the year. But the farther north we are 

 from the equator, the farther around to north does the sun rise 

 and set in summer (making for long days and short nights) . 



Thus if we travel far to the north in summertime, we find the 

 days still longer than they are in the United States. When we get 

 as far north as the capital of Sweden, for example, a summer day 

 is nearly nineteen hours long. Still farther north, beyond the 

 Arctic Circle, there is a time in midsummer when we would find 

 the sun shining continuously for forty-eight hours! 



In wintertime, however, the farther north we are from the 

 equator, the farther to the south does the sun rise and set. This 

 produces short days and long nights. 



What causes these changing lengths of night and days? The 

 earth's axis is tilted and always pointed in the same direction 

 with the North Pole toward the north pole of the sky. There is a 

 certain stage in the journey of the earth around the sun when our 

 North Pole is tipped farthest toward the sun. One result is that 



