QUESTIONS 19 



apparent motions of the stars are owing to the earth's move- 

 ments on its axis and around the sun. 



The ancients grouped the stars into constellations which 

 vaguely represented animals or ancient heroes. Modern 

 astronomers retain these groupings for convenience in study- 

 ing the heavens. 



The sun's family consists of eight planets and their satel- 

 lites or moons, the asteroids, and occasional solar visitors 

 called comets. The planets differ from each other in size, 

 nearness to the sun, temperature, number of satellites, length 

 of orbit, rate of speed, time of rotation, time of revolution, 

 and in many other ways. They shine only by the reflected 

 light of the sun. 



All satellites revolve about the planets they accompany. 

 Our own moon revolves about the earth at an average dis- 

 tance of 240,000 miles. It rotates once on its axis and travels 

 once around the earth in a little less than a month. The 

 moon's revolution about the earth accounts for its changing 

 phases, for eclipses both of the sun and of the moon, and for 

 our ocean tides. 



QUESTIONS 



What are the most impressive facts about the sun ? 



Why do we not see the stars in daytime ? 



How do the planets differ from stars ? 



Why are the lights of the stars so dim to us ? 



Do the stars appear to change their relative positions in the sky 

 from time to time ? What makes them appear to revolve around 

 the earth? 



In what respects do the planets differ from each other ? 



What are the most interesting facts about the moon? What 

 accounts for its changes of appearance ? 



What causes an eclipse of the sun? Of the moon? 



What is a meteorite ? a comet ? a constellation ? 



