CHAPTEK XX. 
CELESTIAL TRAVELERS. 
The sun together with the planets that revolve 
around it constitute our solar system. It is probable 
that every star is the center of a solar system resem¬ 
bling our own, some of them, perhaps, much larger 
than ours. 
The planets of our system are grouped as major 
and minor planets. The major or greater are eight 
in number. In the order of their distance from the 
sun they are Mercury, Yenus, Earth, Mars, Jupiter, 
Saturn, Uranus, and Xeptune. Our planet is the third. 
Yenus and Mercury revolve about the sun, inside the 
earth, and hence are called the inferior planets; those 
whose orbits are outside the earth are superior planets. 
The planets, as far as can be discovered, are very 
much alike in general appearance. Mercury is too 
near the sun, and Xeptune and, indeed, Uranus are 
too far away from the earth to reveal their surface. 
Generally speaking, the planets have a dark, more or 
less variegated band on both sides of their equator, 
shading into a whitish surface about the poles. This 
suggests zones of climate resembling those of the 
earth. Their axes are also inclined, and at angles that 
dhffer little from the angle of the earth’s axis. 
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