THE SURFACE FEATURES OF THE MOON^ 



By F. E. Wright 

 Geophysical Laboratory, Carnegie Institution of Washington 



[Witli 4 plates] 



The moon needs no introduction. It has been known to all of us 

 from early childhood when we first tried to reach out and touch it 

 and later learned to decipher both the man and the lady in the 

 moon. In spite of this general interest and friendly feeling toward 

 the moon, the president of the Carnegie Institution of Washington 

 realized several years ago that its presence in the night sky is re- 

 sented by the modern astronomer, especially the astrophysicist. Its 

 light interferes with the photography and analysis of far-distant, 

 faint celestial objects, such as stars, clusters, and nebulae — incandes- 

 cent masses of enormous size, radiating huge amounts of energy into 

 space and of special significance because they yield information on 

 the extent of the universe and on the behavior and structure of matter 

 under conditions of temperature and pressure not attainable in the 

 laboratory. These remote, active heavenly bodies appeal to the imagi- 

 nation and offer problems of the most fascinating kind for solution. 

 The astrophysicist is occupied with receiving and interpreting their 

 messages. He learns little in this field from the moon. To him it is 

 a lifeless, inert mass, shining only by reflected sunlight and held by 

 gravitation in its orbit about the earth. From an astronomical view- 

 point, the moon is an insignificant object only 2,160 miles in diameter; 

 the sun is nearly a million (864,000) miles in diameter. To us the 

 moon appears large because it is distant only 30 earth's diameters, 

 or 240,000 miles. Viewed through a large telescope it appears to be 

 only 200 or 300 miles away and details 500 feet apart can be dis- 

 tinguished under conditions of good seeing. 



To the layman, not versed in astrophysics, the moon is the most 

 conspicuous object in the night sky and the rival of all heavenly 

 objects, even including the sun itself. It has played a significant 



1 This article presents tlie progress made by tlie committee on study of the surface 

 features of the moon of the Carnegie Institution of Washington, of which the author is 

 chairman. Reprinted by permission from The Scientific Monthly, vol. 40, pp. 101-115, 

 February 1935. 



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