THE MOON, PLANETS, AND COMETS 257 



are great clouds, sometimes one thousand miles across, which 

 develop and disappear in rapid succession (fig. 128). It seems 

 perfectly certain, in view of its primitive condition as well 

 as of its great distance from the sun, that no life can exist 

 upon its surface. 



An interesting consequence of Jupiter's great dimensions 

 and rapid rotation (its day is nine hours and fifty-five minutes) 

 is that it is very much bulged at the equator and flattened 

 at the poles. Its ellipti- 

 cal form and the belts 

 across its surface can be 

 observed by means of tele- 

 scopes a few inches in 

 diameter. 



As might perhaps be 

 expected, Jupiter has a 

 large number of moons. 

 The first four were dis- 

 covered by Galileo in 

 1610 with the first tele- 

 scope used by man to 

 record the facts regard- 

 ing the heavens. These 

 four moons were in fact 

 the first heavenly bodies 

 discovered with the aid of an instrument. The fifth satellite 

 of Jupiter was discovered in 1892, and since then five other 

 small moons have been found. The largest ones are larger 

 than the planet Mercury, and the smallest ones are less than 

 one hundred miles in diameter. The eight which are nearest 

 the planet revolve around it from west to east, which is the 

 direction in which the planet rotates, but the two most remote 

 revolve in the opposite direction. 



The planet Jupiter was visible as a conspicuous object in 

 the eastern sky in the late autumn of 1917 ; it will be visible 



FIG. 128. Jupiter 



Note the cloudlike bands which appear upon 



this planet. Photograph by the Yerkes 



Observatory 



