398 ] Our Earth and Its Fellow Planets 



about the sun requires almost 165 of our years. It has one satellite 

 and, like Uranus, is greenish in color. 



How URANUS AND NEPTUNE WERE DISCOVERED 

 It is interesting to realize that Uranus was discovered purely 

 by accident in 1781 thousands of years after people first began to 

 watch the heavens and firmly concluded there were no planets 

 beyond Saturn. The discoverer of Uranus was Sir William 

 Herschel, a great British astonomer, whose name is sometimes 

 given to it. 



Neptune was found independently in 1846 by two different 

 astronomers each unknown to the other! They noticed that 

 Uranus did not always follow its expected course, and they specu- 

 lated that this might be due to the influence of another, hitherto 

 unknown, planet. After several years of study and calculations, 

 each man in his own way located the "new" planet, which was 

 named Neptune. Science had rung up another curtain, revealed 

 another secret of the mysterious universe that is our home. 



Pluto Most Distant of Them All 



The most recently discovered planet (it was first seen in 1930) , 

 Pluto is completely beyond the range of a small telescope. Small 

 wonder Pluto is almost four billion miles away from us! It is the 

 planet most distant from the sun, and requires nearly 250 of our 

 years to complete one trip around it. 



Pluto does not compare in size to the giant planets, and is prob- 

 ably somewhat smaller than the earth. One interesting theory 

 about the origin of Pluto is that it may have started as an escaped 

 satellite of its nearest planetary neighbor, Neptune. Scientists 

 believe that Pluto has little or no atmosphere, as it reflects light 

 very poorly. Pluto is yellowish in color. 



Though this planet was named for the god of the underworld, 

 the first two letters PL are used for its symbol, and these are the 

 initials of a great astronomer, Percival Lowell. It was Dr. Lowell 

 who calculated how a planet in the realm of Pluto must move. 



