ASTEROIDS AND SATELLITES. 



489 



approximately be obtained. The dates of the discovery of the more 

 modern pair are added : 



Altogether there are a great number of planets and asteroids, which 

 latter are minor planets circulating outside the orbit of Mars. They have 

 nearly all classical names, such as Juno, Ceres, Vesta, Flora, Ariadne, Pallas, 

 Pomona, Thalia, etc., and are all at distances from the sun ranging between 

 200,000,000 and 300,000,000 of miles, the periods of sidereal revolution 

 ranging from 1,100 to 3,000 days, so their years must be from four times to 

 nine times as long as ours. Altogether about two hundred of the minor 



Fig- 532. Mars. 



planets have been discovered, and they are all very much smaller than the 

 earth ; some, indeed, being very tiny only a few miles in diameter, but very 

 massive. They do not appear to possess any satellites at least, none have 

 been discovered, for such very small bodies as they must be, supposing they 

 exist, would be quite invisible even with our perfected instruments. 



SATELLITES, however, or " planetary moons," as they are sometimes 

 designated, are plainly perceived attending upon the great planets. There 

 arc twenty of these at present under observation. One we are all familiar 

 with, and the moon, par excellence, lends a beauty to our nights which no other 



