36 FIRST YEAR COURSE IN GENERAL SCIENCE 



the sun in the same period, each planet would always be 

 seen in the same place, with relation to the others; but 

 when the earth has gone around the sun once, Venus has 

 gone about one and two-thirds times around, while Mars 

 has gone about half-way around. 



25. Why the Planets Shine. The stars shine because 

 they are white-hot, but the planets are bright because 

 the sun's light falls on them and a part of it is 

 reflected to us. A mirror can be made to reflect nearly 

 all the light that falls upon it. The planets, however, 

 reflect only about half the light they receive from the 

 sun. If the earth were seen from one of the planets, it 

 would probably appear very nearly as bright as the planets 

 look to us. 



26. The Size of the Planets and their Distances from 

 the Sun. Venus is nearly as large as the earth ; Mars is 

 smaller than the earth; Saturn is many times as large; and 

 Jupiter is as large as all the others put together. Mercury 

 is much smaller than the earth, and Uranus and Neptune 

 are about four times as large as the earth. 



The distances of the planets from the sun differ greatly. 

 The smallest planets are nearest to the sun. We know the 

 earth to be nearly 93,000,000 miles from the sun. Mercury 

 is .4 of that distance from the sun and Venus .7. Mars is 

 1.5 times as far away; and Jupiter is 5, Saturn 9, Uranus 

 19, and Neptune 30 times as far from the sun as the earth 

 is. Mercury is so near the sun that it is usually in the sky 

 in the daytime. Uranus and Neptune, because of their 

 great distance, seem like stars of the sixth and ninth 

 magnitude respectively. (LABORATORY MANUAL, Exercise 



in.) 



27. Venus. Venus is so like the earth in size and dis- 

 tance from the sun that it is sometimes called the earth's 

 twin planet. No one can tell whether it has continents and 

 oceans, mountains and plains. Its surface cannot be clearly 



