TUB OPEN SKY 



To get an idea of the relative sizes of the earth and sun, 

 draw a circle an eighth of an inch in diameter to represent 

 the earth and alongside of it a circle of a little more than 

 thirteen and one-half inches in diameter to represent the sun. 

 The diameter of the earth is about 8000 miles, and the di- 

 ameter of the sun is approximately 866,000 miles. Imagine 

 that the sun were hollow and that the earth could be placed 

 at the center of this hollow sphere, with the moon just as far 

 away from us as it now is about 240,000 miles. The moon 

 would also be inside the hollow sphere and almost as far away 

 from its surface as from the earth. The sun is made up of 

 more than 300,000 times as much matter as there is in the 

 earth, and it occupies more than 1,300,000 times as much 

 space. 



Astronomers see the surface of the sun as a wild tumult of 

 raging flame. The outside layers are made up wholly of 

 incandescent gases ; but the interior, because of the enormous 

 pressure upon it, must be in a molten or solid condition. Stu- 

 pendous eruptions and tempests of flame constantly rend its 

 surface, causing incandescent gases to shoot up for hundreds 

 of thousands of miles. Sometimes furious whirling storms of 

 vast diameter occur. These often continue for long periods 

 of time, and appear to observers on the earth as sun spots. 



On account of the enormous amount of heat and light 

 given out by the sun, it is well for us that the earth keeps 

 at an average distance of about 93,000,000 miles from the 

 sun. This distance is so great that we can have no ad- 

 equate appreciation of it. If an express train which could 

 travel the distance of the earth's circumference in about 

 thirty-five days, could start off into space and travel day and 

 night at the same steady speed in a straight line to the sun, 

 it would require more than 350 years to reach its destination. 



