PLATE XX. 



COPERNICUS AND SURROUNDINGS. PHOTOGRAPHED BY RITCHEY, NOVEMBER 21, 



igOl, 7 HOURS 32 MINUTES P.M., CENTRAL STANDARD TIME. EXPOSURE, 



ONE SECOND. SCALE, THREE-FOURTHS METER TO MOON'S DIAMETER. 



This plate of Copernicus should be compared with the plates showing the same, structure 

 under more nearly vertical illumination when the light bands appear. 



In the plate the lower level area is a part of the Mare Imbrium. This is bordered on the left 

 by a portion of the high country known as the Apennines, which extend as far towards the center 

 of the plate as the large crater Eratosthenes. To the left, separated by a little more than the 

 width of Copernicus, is the faintly outlined vulcanoid known as Stadius, which appears to have been 

 in large part melted down by the lava of the Oceanus Procellarum which has invaded this field. 

 On the right hand from Eratosthenes, the margin of the mare is formed by the peaks of the 

 Carpathian Mountains. Immediately above Copernicus is a small, double crater, one of the 

 simpler crater valleys. 



The area about Copernicus exhibits several very interesting types of structure. The Carpa- 

 thian Mountains show the mare penetrating into several rude craters, the seaward faces of which 

 have had their walls destroyed by the fluid lava. A broken line of small craters lies midway 

 between Copernicus and Eratosthenes. At either end it verges into a narrow crater valley of the 

 " rill " type. The central part of the upper half of the field abounds in very perfect cones 

 which are associated with small crater pits. 



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