JUPITER. 



17 



miles in diameter, and placed at the enormous distance of 



191,000,000 miles from the sun. This great planet takes 



12 years and 52 days to perform its circuit ; it turns upon 



its axis in 9 hours 55 minutes, a 



surprisingly short time considering 



the immensity of its bulk. As a 



result of this rapid motion Jupiter 



is very far removed from the form of 



a true sphere, for the oblate form 



of heavenly bodies is caused by their 



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FIG. Iti. 



FIG. 17. 



rotatory motion, and the centrifugal 

 force set up by it. In fig. 16 is an 

 outline of the earth and Jupiter, 

 showing their relative size. It has 

 no phases, like those planets which 

 are nearer to the sun than the earth, 

 its great distance preventing this, as 

 may be seen in fig. 17, in which 

 the earth (E E) is placed at the two widest lateral positions 

 of its orbit, but the earth is too near the sun, in pro- 

 portion to the great distance of Jupiter, to allow any part 

 of the latter to come within the range of vision, except that 

 which is illuminated by the sun. This planet is high up in 

 the heavens the greater number of nights in the year, and is 

 therefore a very conspicuous object. It also presents a 



