THE JOVIAN SYSTEM. 



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planet. His inclination is very small, and you now know that under such 

 circumstances he enjoys very small changes of seasons. Jupiter has four 

 moons, or satellites, and an illustration of the " Jovian System " is herewith 

 given. 



Jupiter himself was well known to the ancients, but Galileo was the 

 discoverer of the " moons." His telescope was, of course, a very imperfect 

 instrument, and while he was gazing at the planet he noticed three stars 

 close by the bright disc, two on one side, but next day Galileo perceived 



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Fig. 586. The Jovian System 



them all at the same side. Next time he looked there were only two, and 

 after many anxious observations he found out, not only that Jupiter had three 

 attendant stars, but four ! 



These moons were found to revolve round Jupiter in times varying from 

 nearly two days to nearly sixteen days, according as they were at a less or 

 greater distance from him. They were found to have their times of eclipses 

 and transits, etc., also. These moons act with respect to Jupiter very much 

 as the inner planets act with respect to the sun, for observation showed 



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