SUMMARY 15 



earth than do any other bodies. The sun gives us energy 

 in the form of light and heat and so maintains all the life 

 upon the earth. The moon, though shining only by light 

 reflected from the sun, exerts a great attraction upon the 

 earth, causing the tides, which help to keep the waters 

 of our harbors clean. 



QUESTIONS 



Why do we see no stars in the daytime? 



How is the appearance of the stars explained? 



What is the difference between stars and planets ? 



What starlike bodies make up the solar system ? 



Name and illustrate three universal properties of matter. 



What daily experiences of yours are explained by these properties ? 



What forces keep the moon moving around the earth in its orbit? 



Draw circles illustrative of the size of the earth, moon, and sun. 



Why are the sun and moon particularly interesting to us ? 



How long would it take an express train running thirty miles an 

 hour and stopping neither day nor night to go over the distance from 

 the earth to the moon ? From the earth to the sun ? 



