166 Our Surroundings 



The sun is the center of the solar system, and is the largest 

 body in it. 



There are various theories in regard to the composition of 

 the sun, of which KirchofFs is the most generally accepted. 



The sun provides radiant energy, that is, heat and light. It is 

 the source of most of the energy in the solar system. 



The earth is one of the planets. It revolves around the sun, 

 making a complete revolution in 365 X days. 



The moon in her revolution around the earth presents different 

 phases. 



The principal causes of the change of seasons on the earth 

 are the inclination of the earth's axis, its yearly revolution around 

 the sun, and its distance from the sun. 



A solar eclipse occurs when the moon passes between the earth 

 and the sun. 



Latitude is the distance north or south of the equator, and 

 longitude is the distance east or west of a prime meridian. 



Standard time refers to a system of time adopted by the United 

 States government. 



Stars are bodies in the heavens which form the starry system. 

 Certain groups of stars make up constellations. 



Among the principal constellations are the Great Bear, the 

 Little Bear, Lyra, Cassiopeia, and the Pleiades. 



The milky way is a luminous, cloud-like band in the heavens 

 composed of a vast number of stars. 



Twinkling of the stars is due to atmospheric conditions which 

 magnify or diminish the light they send to the earth. 



FACT AND THOUGHT QUESTIONS 



1. What is included in the term "the heavens"? 



2. Name several ways in which knowledge of the heavens is of value 

 to man. 



3. Describe Kirchoff's theory in regard to the composition of the sun. 



4. What does the sun supply? 



5. Mention the causes of the change of seasons on the earth. 



6. What is the season in the Argentine republic during our mid-summer? 



7. Give the cause of the phases of the moon. 



8. What causes an eclipse of the sun? 



9. Define: (a) latitude; (b) longitude. 



