396 ] Our Earth and Its Fellow Planets 



believe that the atmosphere of Jupiter is thousands of miles deep 

 and that the solid core of the planet is comparatively small. 



JUPITER HAS MOONS 



What is possibly the most interesting feature of Jupiter, 

 the procession of moons that circle about the planet, cannot be 

 seen with the naked eye. There are twelve of these moons four of 

 them visible through powerful field glasses. Looking at these four 

 through a small telescope, you may see them circling around 

 Jupiter, first in front of, then vanishing behind, the giant planet. 

 It was about 350 years ago that the great Galileo discovered these 

 four moons, which are about the size of our own moon. They 

 were the first moons ever seen that belonged to any other planet 

 than the earth. The development of more powerful telescopes led 

 to the discovery of eight smaller moons around Jupiter, the most 

 recent one coming in 1951. 



Saturn and Its Strange, Gigantic Rings 



This planet, too, has moons, but it has an even more fascinating 

 feature. Saturn is encircled by three strange, gigantic rings that 

 whirl around it continually. These rings are one of the unsolved 

 mysteries of astronomy. Why should Saturn but no other planet- 

 have rings? 



The rings of Saturn are not solid they are apparently made up 

 of innumerable tiny particles, perhaps no larger than grains of 

 dust. These great rings are probably not more than ten miles 

 thick which is paper-thin in relation to its enormous diameter. 



LOOKING AT SATURN'S RINGS 



If we view Saturn through a small telescope, we see the 

 rings as a single flattened object. However, a more powerful instru- 

 ment reveals all three of them, one inside the other. The inner- 

 most ring is very faint; the middle one is the brightest. They are 

 inclined at an angle that is unchanging, but, as the planet moves 

 around the sun we see them at varying angles according to Saturn's 

 position with respect to the earth. 



