Man's physical universe

xanabras

108 THE UNIVERSE A VAST SYSTEM OF PARTS

has been estimated to be not more than ten miles thick.

These rings

consist of small particles. According to one hypothesis, the rings

came into existence as the result of

tidal forces set up in a large satellite

which came too near the planet.

Saturn has nine moons, the largest

of which. Titan, is larger than our

moon, while the smallest, Phoebe,

is only about 150 miles in diameter.

Phoebe was the first moon of

Fig. 28. Saturn. (Photograph any planet whose direction of revofrom

the Yerkes Observatory, re-

^^^-^^ ^^^ observed to be counter

printed by permission ot the Chicago

r i i /-. t^

to that of the planet. On December

16, 1943, Saturn will be in

University Press.)

the

best position for observation in

the northern hemisphere, showing its

widest opening of the rings at a time of maximum brilliancy.

Uranus Was Discovered by Accident.

Sir William Ilerschel (1738-1822), his sister Caroline (1750-1848),

and his son John (1792-1871) made many contributions to astronomy.

Sir William was a musician of unusual ability and made his living with

his music. Astronomy was his hobby and he spent all of his spare time

and money making telescopes and observing the sky. On the night of

March 13, 1781, Herschel discovered Uranus when he happened by

chance to be observing that portion of the heavens occupied by that

planet.

The ancients did not know of the existence of any of the planets

beyond Saturn, but modern astronomers have found three other

planets, the most distant one being at a distance four times as great as

the distance from the sun to Saturn.

It does not seem possible that either Saturn or Uranus could support

life of any kind. Our chief interest in Uranus is in connection with the

discovery of Neptune in the position predicted from observed discrepancies

in the motion of Uranus.

The Discovery of Neptune Was a Triumph of Scientific Theory.

Newton's laws enable man to compute the paths of the heavenly

bodies with amazing accuracy.

Uranus followed its predicted path until 1831, when its deviation

began to be enough to observe. By 1841 the discrepancies were so

great that one of two conclusions had to be drawn; either Newton's

laws were not correct, or there was an unknown body influencing the

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