250 Trees, Stars, and Birds 



planet itself. Both Saturn and Jupiter may be so hot 

 that they consist entirely of vapors. Saturn is nearly 

 800 times as large as the earth and only 95 times as 

 heavy, with a density only one eighth that of the earth. 

 Satellites of Saturn. Saturn has eight moons that 

 have been known for a long time. A ninth one was dis- 

 covered in 1899 on a photograph taken the previous 

 year at the Harvard Observatory at Arequipa, Peru, 

 by Professor W. H. Pickering, who named it Phoebe. 

 To see so small an object at such a distance is like see- 

 ing from the National Capital a humming bird in Cen- 

 tral Park, New York. 



Saturn, like the earth, rotates from west to east, and 

 most of its moons revolve about it in the same direc- 

 tion ; but Phcebe, the most distant of its satellites, re- 

 volves from east to west. 



Rings of Saturn. More wonderful than its moons 

 are the brilliant rings that surround this planet. These 

 may usually be seen with a small telescope, though at 

 times a large one is required to make them visible. 

 Galileo, who saw them in 1610 without understanding 



what they were, was 

 much puzzled ; for when 

 he looked for them a 

 while afterward he could 

 not see them at all. 

 The explanation is 

 simple. The rings are 

 flat, like a sheet- of 



FIG. 150. A photograph of Saturn show- r Qr car dboard I 



ing the rings turned partly toward the r r 



earth. when the sides of the 



