The Romance of the Heavens 31 



2 



Jupiter and Saturn 



Next to Mars, going outward from the sun, is Jupiter. Be- 

 tween Mars and Jupiter, however, there are more than three 

 hundred million miles of space, and the older astronomers won- 

 dered why this was not occupied by a planet. We now know that 

 it contains about nine hundred "planetoids," or small globes of 

 from five to five hundred miles in diameter. It was at one time 

 thought that a planet might have burst into these fragments (a 

 theory wjhich is not mathematically satisfactory) , or it may be that 

 the material which is scattered in them was prevented by the near- 

 ness of the great bulk of Jupiter from uniting into one globe. 



For Jupiter is a giant planet, and its gravitational influence 

 must extend far over space. It is 1,300 times as large as the 

 earth, and has nine moons, four of which are large, in attendance 

 on it. It is interesting to note that the outermost moons of Jupi- 

 ter and Saturn revolve round these planets in a direction contrary 

 to the usual direction taken by moons round planets, and by 

 planets round the sun. But there is no life on Jupiter. 



The surface which we see in photographs (Fig. 12) is a mass 

 of cloud or steam which always envelops the body of the planet. 

 It is apparently red-hot. A red tinge is seen sometimes at the 

 edges of its cloud-belts, and a large red region (the "red spot"), 

 23,000 miles in length, has been visible on it for half a century. 

 There may be a liquid or solid core to the planet, but as a whole 

 it is a mass of seething vapours whirling round on its axis once in 

 every ten hours. As in the case of the sun, however, different 

 latitudes appear to rotate at different rates. The interior of 

 Jupiter is very hot, but the planet is not self-luminous. The 

 planets Venus and Jupiter shine very brightly, but they have no 

 light of their own ; they reflect the sunlight. 



Saturn is in the same interesting condition. The surface in 

 the photograph (Fig. 13) is steam, and Saturn is so far away 



