10 EXPERIMENTAL GENERAL SCIENCE 



see the fully illuminated half of the moon, we call it full moon. 

 When only part of the moon is visible it may appear as a cres- 

 cent. The new moon always appears in the western sky shortly 

 after sunset. To an observer on the moon, the earth would 

 appear exactly like a larger and brighter moon. The fact that 

 the earth really does shine to the other planets may be realized 

 when, as occasionally occurs, the whole moon is faintly outlined 

 at the time of new moon. Since the bright crescent is the 

 only part that reflects the sun's rays, the faint illumination of 

 the rest of the surface must be due to earthshine. This appear- 

 ance is frequently spoken of as the "old moon in the new 

 moon's arms." 



15. Eclipses. An eclipse always occurs when a body 

 comes between any of the heavenly bodies and their source of 

 light. Eclipses of the moon, therefore, are caused by the 

 earth coming between the moon and the sun. The moon 

 passes into the earth's shadow and is totally or partially 

 eclipsed. Eclipses of the sun are due to the .passing of the 

 earth through the moon's shadow; that is, the moon passes 

 between us and the sun, cutting off the sun's light from us. To 

 an observer on the sun, this would appear as an eclipse of the 

 earth. The reason why we do not have eclipses of the moon 

 more frequently is because its path about the earth is not in a 

 plane parallel to the earth's orbit and does not dip into the 

 earth's shadow on each revolution. 



16. Shooting Stars and Comets. On a clear night, we may 

 often see what appears to be a star falling toward the earth. 

 The stars, however, do not fall. What seems to be a falling 

 star is really a small particle of matter which our earth has 

 encountered in its travels through space, and which has become 

 so hot from rubbing against our atmosphere that it shines. 

 Such- bodies are often called shooting stars, or meteorites. They 

 usually consist of iron or stone. Great numbers of meteorites 

 come into our atmosphere annually, but most of them burn up 



