382 ] Our Earth and Its Fellow Planets 



planets inhabited by humans, and present "new" planets to 

 explore. 



The imaginative child who accepts and thrills to this fantasy is 

 reassured to learn that at least some of it may become reality. For, 

 since scientists have learned how to use the energy inside the 

 atom, they seriously predict that atomic-energy-propelled rocket- 

 ships may in due course be sent to the moon. So, what only a few 

 years ago would have been regarded as completely fantastic is 

 today given serious consideration. 



Yet these fanciful facts are so intermingled with out-and-out 

 fantasy in young minds that we are actually bringing our children 

 down to earth in more than one sense! when we tell them the 

 truth, as we know it today, about planets and stars. 



LOOKING AT THE SKY 



Though the people of long ago watched the skies closely 

 and made keen observations, they could not understand many 

 things because they assumed that the earth stood still while the 

 planets and stars moved around it. Only about 350 years ago the 

 great Polish astronomer. Copernicus announced his startling hypo- 

 thesis: The movements of the planets became understandable if 

 the earth was a planet and if all the planets revolved about the 

 sun. Copernicus added that the earth also turns on its axis once a 

 day. Thus, while we are apparently watching heavenly bodies 

 move from east to west, we are instead seeing the effects of the 

 earth whirling eastward on its axis. 



Galaxies and More Galaxies: We call the earth and its eight fellow 

 planets that travel around the sun, the "solar system." Beyond 

 our solar system a seemingly endless distance beyond it there are 

 billions of stars! All these heavenly bodies are a part of our 

 universe, or galaxy. At one time, universe (meaning "everything 

 there is, combined into one") seemed a suitable word to use for 

 our galaxy; but, as exploration of the heavens continued, astrono- 

 mers found that our universe was not "everything." Many other 

 galaxies of stars are scattered throughout the endless space that 

 surrounds our own galaxy! 



