Marvels of the Universe 



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Now it might be thought that bj" watching the spots as the planet spins round it would be easy 

 to find out exactly how long the planet's day is. But this is not so ; partly because the markings 

 we see are not solid or permanent features, but cloud-like forms which are constantly changing 

 their shapes and places, and parti}' because the time it takes a spot to go round and come back 

 again into \'iew depends on its distance from the equator. This is very interesting, for it means 

 that Jupiter, as we see it, does not rotate " all of a piece " like the Earth or anj' solid globe, 

 but that the length of the day varies with the place on the planet's surface. If the Earth behaved 

 like this, of course no permanent maps would be possible, for continents and islands and oceans 

 would be perpetually changing their shapes and positions. In the case of Jupiter no part takes so 

 long as ten hours to rotate, and equatorial spots perform their daily journey in about nine hours, 

 fifty and a half minutes, though the time is somewhat variable. It follows that whereas a spot on 

 the Earth's equator is carried round at a speed of about seventeen and a quarter miles a minute, 

 a spot similarly placed on Jupiter has a velocity of nearly four hundred and seventy miles a minute, 

 or well o\'er twenty-eight thousand miles an hour ! 



The belts of Jupiter often show very beautiful and diverse colours. Reds and browns and 

 purples and blues are not uncommonlv to be found, and these, like the forms of the markings, are 

 subject to gradual change. 



But although change is the law of this planet, yet from time to time certain objects appear which 

 last for many years. The most famous of these is the Great Red Spot, which was so conspicuous 

 in 1878 and the years following, and which, though subsequently becoming very faint, has lately 

 shown marked signs of revival. It is perhaps hidden at times by overlying clouds, but it is quite 

 likely that it is identical with objects seen at various times during the last century, and perhaps 

 with one seen by Hooke so long ago as 1664. Xaturallv many speculations have been made as 



[/ju r. E. II. riiiiii/ii, F.ii.A.s. 

 JUPITER. 



Such is the appearance of Jupiter when viewed through a powerful telescope. It is so luminant thai it shows only a 

 bright disc and no spherical shape. Four of its eight attendant moons are visible, but are so far away that they appear only 

 as small dots. 



