402 ] O ur Earth and Its Fellow Planets 



These things we know about the moon, but many others we do 

 not. Its first explorers will doubtless find out much we on earth 

 cannot possibly discover even with our wonderful scientific instru- 

 ments. 



How THE MOON WAS FORMED 



Satellites are generally very tiny in relation to the size of 

 the parent bodies around which they revolve. The other planets, 

 for example, have several hundred thousand times the mass of 

 their satellites. But the moon is an exception: Our earth has only 

 eighty-one times the mass of the moon. One explanation of this is 

 found in the theory that our moon separated from the earth at a 

 comparatively late stage of the earth's development, when it had 

 cooled to a liquid form. 



At this point, so runs the theory, gravitational forces from the 

 sun acted to form a bulge on our earth. In time this bulge sepa- 

 rated as a giant teardrop and moved out into space to occupy its 

 present orbit encircling the earth. Held in its orbit by the con- 

 tinual pulling force of the sun as well as by that of the earth, the 

 moon exerts its own pull on the earth. (This pull of the moon is 

 reflected in our tides. The highest tides each month come with the 

 full moon and the new moon.) 



To support this interesting theory the astronomers have brought 

 geology to their aid by suggesting that the moon's tearing away 

 from the earth left a visible scar on our planet. The fact that the 

 entire Pacific Ocean basin has a different surface rock structure- 

 basalt rather than the granite common to other areas has led some 

 scientists to accept this area as the region where the moon carried 

 away a large portion of our forming earth. 



WHY WE HAVE ECLIPSES OF THE MOON 



Every once in a while the moon stages a show that fascinates 

 children as well as adults. This happens at the times when the 

 moon goes into the shadow of the earth, and we say there has been 

 an eclipse of the moon. 



