326 GENERAL SCIENCE ' 



then touches the earth and causes a dark area which we call the 

 eclipse of the sun. 



Shadows are divided into two parts; a dark center called the 



V . .^ ~~~- v 



FIG. 195. Eclipse of the sun. 



umbra, and a border on all sides of the umbra of a much lighter 

 fringe called the penumbra. 



QUESTIONS 



1. Why do you cast a shadow? 



2. Why are shadows longer in the afternoon than at noon? 



3. Why are shadows so short at noon? 



4. Where on the earth would a shadow always be of the same 

 length? 



5. What causes an eclipse? What is a partial eclipse?, 

 ' 6. Why are clouds sometimes black? 



7. Why do stars twinkle? Why do planets glow with a steady light? 



8. How do scientists know that there are vibrations which do 

 not cause any sensation upon the nerve centers of human beings? 



9. How are silhouettes made? ^ 



10. Why is a shadow behind us when we are facing the light 

 and in front of us when the light is at our backs? 



11. Can a piece of glass be made to cast a shadow? . Explain. 



12. Will a shadow increase or decrease in size when one holds 

 on object nearer to the light? 



