250 ELEMENTS OF GENERAL SCIENCE 



eclipse of the sun. For persons in the path of the shadow 

 the sun's light is cut off (fig. 125), and for a short time, 

 usually only a minute or two, the sun is invisible. 



The accuracy with which astronomers know the distance, 

 dimensions, and motions of the moon is shown by the fact 

 that they are able to predict with a high degree of accuracy 



FIG. 125. The sun at total eclipse 



The picture shows the crown, or corona, around the sun. Photograph by the 

 Yerkes Observatory 



when eclipses will occur. It can be determined when an 

 eclipse will occur and from what points on the earth's sur- 

 face it will be visible. Computations of eclipses are made 

 many years in advance, and astronomers organize and equip 

 expeditions at great expense to go to favorable places for 

 observing them. 



Eclipses of the sun have been used in the most interesting 

 manner to locate in our system of counting time some of the 



