152 Our Surroundings 



the lighted candle represents the sun. Place the candle on the 

 board a little to the right of the center of the long axis of the 

 ellipse. Locate the point at the extreme left of the long axis 

 of the ellipse. Call this point A. Locate the point at the extreme 

 right of the long axis. Call this point C. Locate the two points 

 on the ellipse halfway between A and C. With A at your left, 

 call the point nearest you B, and the opposite one D. 



Place the globe at A. At A the axis of the globe should point 

 along the long axis of the ellipse with the top toward the center 

 of the ellipse. When the globe is at A, it represents the position 

 of the earth with reference to the sun on June 21 of each year, 

 and the season is summer north of the equator. Now move the 

 globe along the line of the ellipse to the point B, never changing 

 the direction of the axis of the globe. This represents the posi- 

 tion of the earth on September 22 of each year, and the season 

 is autumn north of the equator. Next move the globe to C. The 

 earth is in this position with reference to the sun on December 

 22. The season is winter north of the equator, and the earth has 

 traveled through one-half of its orbit. Placing the globe at D 

 shows the earth's position on each March 21, and it is spring 



north of the equator. When 

 the globe has traveled back to 

 A it has made a complete revo- 

 lution around the light which 

 represents the sun. This shows 

 the yearly motion of the earth 

 in its orbit. 



While the earth is traveling 

 around the sun once each year, 

 the moon is traveling around 

 the earth once in about each 



L. E. Knott Apparatus Co. or k T / J 0*^1 > 



A TV/T 29^/2 days. Since the moon s 



APPARATUS TO SHOW RELATIVE MOVE- / 2 y . 



MENTS OF THE EARTH AND THE orbit circles the earth, it is 

 MOON AROUND THE SUN dear that the moon also j our _ 



neys around the sun once in each year. 



The apparatus illustrated above shows the motions of the 

 earth and the moon around the sun. As the globe, which repre- 



