Man's physical universe

xanabras

THE PLANETS AND THEIR MOTIONS 109

path of Uranus. Two mathematicians, J. C. Adams and U. J. J. Leverrier,

working independently, calculated the position of this unknown

body; and in 1846 the German astronomer, Dr. J. G. Galle, whom

Leverrier asked to look for it, after a half-hour's search, discovered the

planet Neptune less than a degree distant from the predicted position.

This was a great triumph for Newton's laws and greatly increased

man's belief that his universe is one of cause and effect.

Neptune is the third largest planet and has only one satellite, which

rotates in a direction counter to that of the planet itself. This moon is

noteworthy in that it is larger than the planet Mars.

Pluto Is the Most Remote Planet.

The planet Pluto was discovered at the Lowell Observatory on

January 21, 1930. Lowell, who died in 1916, and other astronomers had

predicted the existence of this additional planet on the basis of exceedingly

minute discrepancies in

the path of Uranus that even the discovery

of Neptune did not completely explain. It required a long time

to discover Pluto because it is no brighter than 15,000,000 stars from

which it had to be distinguished.

This discovery not only added to the confidence of astronomers in

Newton's laws but also was a triumph for modern methods, for it had

to be searched for photographically. Photography had begun to

develop in Sir William Herschel's time, but comparisons of the motion

pictures of today with those taken twenty years ago are sufficient to

show the amazing progress which has been made in this field in our own

generation.

Pluto is thought to be inferior to the earth in mass and size. It is

about 3,670,000,000 miles from the sun, and it is estimated that its

period of revolution around the sun is about 248 years.

STUDY QUESTIONS

1. Explain how the day and year on the planet Mercury can be the same.

2. Why does Mercury have such great extremes of temperature?

3. What peculiar feature is associated with the planet Saturn?

4. In what respect was the discovery of Neptune a scientific triumph?

5. What are Planetoids or Asteroids?

6. Discuss planetary moons briefly as to size, direction of rotation, number,

and speed.

7. Would it be possible to see a skyscraper on the moon with a modern telescope?

8.

9.

Why is it that a high jumper could jump forty feet on the moon?

Why are the mountains on the moon steep and jagged?

10. What is a possible cause of the craters on the moon?