The Heavens 165 



the irregular passage of these beams through the air due to the 

 unequal density, humidity and warmth of the different strata, or 

 layers, of the atmosphere. As these layers of air pass between 

 the observer and the star, the light may be alternately magnified 

 and diminished. 



Distance in the Heavens. We have no conception of the 

 great distances to many of the stars we see at night. Most of the 

 stars are so far away that if these distances were measured in 

 miles the figures would mean little to us. A new unit of measure 

 has been devised to express these great spaces between the earth 

 and the stars. This unit is the light year. The light year is the 

 distance that light will travel in one year. Light travels 186,000 

 miles, about 7^ times the distance around the earth, in one 

 second. Yet even at this terrific rate of speed it takes years for 

 light to come to us from the nearest star. Some stars are 

 so far away that light from them travels many thousand years 

 before reaching the earth. No one can imagine these great dis- 

 tances. It is also probable that there are many more stars 



Wide World Photo. 



DISTANCE IN THE HEAVENS 



Aldebaran is one of the nearest stars, yet the light we get from it today left it 



44 years ago. 



much farther away than those we have seen, for with each im- 

 provement of the telescope new and more distant ones come into 

 view. 



SUMMARY 



The heavens include all the parts of the solar and the starry 

 systems. 



