390 ] Our Earth and Its Fellow Planets 



this story was broadcast on a Sunday evening in 1938, the narra- 

 tion was so "realistic" that great numbers of people were caught 

 in the unreasoning grip of hysteria. The popular reaction to this 

 broadcast is the most convincing proof that scientific knowledge 

 of the planets is not very widespread. Their distance is so great, 

 of course, that no object could proceed from them toward our 

 planet without its movements being noticed long in advance of its 

 arrival. 



Mercury Submerged by the Sun's Brilliance 



Though Mars is probably our most frequently discussed planet 

 neighbor, Venus and Mercury are also reasonably close close, that 

 is, in comparison to the other five remaining planets. Together 

 with Earth and Mars, they are sometimes called the "terrestrial 

 planets." All are made up of solid, fairly heavy material. All are 

 roughly comparable in size, and all rotate on their axis at moderate 

 or slow speed. 



LIFE is IMPOSSIBLE ON MERCURY 



The smallest member of the sun's "family," Mercury is also 

 closest to the sun. Because of its small size and slight mass (it is 

 only three thousand miles in diameter and the earth has twenty- 

 five times as much mass) , the attraction of gravity on its surface 

 is not enough to retain an atmosphere. And because of its nearness 

 to the sun, Mercury's surface is hot. The heat and lack of atmos- 

 phere make life impossible. 



WHEN MERCURY is VISIBLE 



Submerged by the sun's brilliance, Mercury is generally 

 invisible to us. During the year there are only six periods of two 

 weeks' duration when we can see it clearly, shining with a white 

 light. These are the times when it is farthest, east or west, from 

 the sun as seen from the earth. When it is far to the east of the 

 sun, Mercury sets soon after the sun. We then see it in the west, 

 and know it as the "evening star." About two months later, when 

 Mercury is farthest to the west of the sun, it rises in the east a 



