130 ANSWERS TO PRACTICAL QUESTIONS 



77. How can you detect the yearly motion of the sun 

 among the stars ? 



(See Astronomy, first note, p. 94.) 



78. Have you actually traced the movement of any one 

 of the planets, so as to understand its peculiar and irregu- 

 lar wandering among the stars ? 



Pupils should be encouraged to watch the various move- 

 ments of the heavenly bodies. Read a thoughtful and sug- 

 gestive article upon Astronomy in High Schools, in Popular 

 Science Monthly, Vol. xx., p. 300. 



79. Hoiv do you explain the varied aspect of the heav- 

 ens in the different seasons of the year ? 



(See Astronomy, p. 92.) 



80. How does the spinning of a top illustrate the sub- 

 ject of precession? 



(See Astronomy, p. 109.) 



81. Why do solar eclipses come on from the west and 

 cross to the east, while lunar eclipses come on from the east 

 and cross to the west ? 



The moon is moving from west to east around the earth. 

 In a solar eclipse, her shadow first strikes the western edge of 

 the sun ; in a lunar eclipse, the eastern edge of the moon first 

 strikes the shadow of the earth. 



The monthly motion of the moon from west to east should 

 be carefully distinguished from the daily motion caused by the 

 earth's rotation. 



82. Newcomb, in his Astronomy, says that, " If, when 

 the inoon is near the meridian, an observer could in a mo- 

 ment jump from New York to Liverpool, keeping his eye 

 fioced upon that body, he could see her apparently jump in 

 the opposite direction about the same distance." Explain. 



This is an illustration of transferred motion. 



83. Wlien, and by whom, was the basis of the calendar 

 we now use fully established ? 



The Koman calendar had become involved in confusion, 



