ASTRONOMY WITH AN OPERA-GLASS. 



487 



of different material from that of which the most of the moon's sur- 

 face is composed a material possessing a higher reflective power. In 

 this respect they resemble Aristarchus and other lunar craters that 

 are remarkable for their brilliancy under a high illumination. Tycho 

 itself, the center or hub, from which these streaks radiate like spokes, 

 is very brilliant in the full moon. But immediately around Tycho 

 there is a dark rim some twenty-live miles broad. Beyond this rim 

 the surface becomes bright, and the bright region extends about ninety 

 miles farther. Out of it spring the great rays or streaks which vary 

 from ten to twenty miles in width, and many of which are several 

 hundred miles long one, which we have already mentioned as extend- 

 ing across the Sea of Serenity, being upward of two thousand miles 

 in length. It has been truly said that we have nothing like these 

 streaks upon the earth, and so there is no analogy to go by in trying 

 to determine their nature. It has been suggested that if the moon had 

 been split or shattered from within by some tremendous force, and 

 molten matter from the interior had been thrust up into the cracks 

 thus formed, and had cooled there into broad seams of rock, possessing 

 a higher reflective power than the surrounding surface of the moon, 

 then the appearances presented would not be unlike what we actually 

 see. But there are serious objections to such a view, which we have 

 not space to discuss here. It is 

 enough to say that the nature of 

 these streaks is still a question 

 awaiting solution, and here is an 

 opportunity for an important dis- 

 covery, but one not to be achieved 

 with an opera-glass. 



Clavius (It) is one of the most 

 impressive of all the lunar forma- 

 tions. There probably does not 

 exist anywhere upon the earth so 

 wild a scene upon a correspond- 

 ing scale of grandeur. Of course, 

 its details are far beyond the reach 

 of the instrument we are supposed 

 to be using, and yet even with a 

 field -glass, or a powerful opera- 

 glass, some of its main features 

 are visible. It is represented in our third illustration, being the low- 

 est and largest of the ring-like forms seen at the inner edge of the 

 illuminated half of the disk ; the rays of the rising sun touching 

 the summits of some of the peaks in its interior have brought them 

 into sight as a point of light, and at the same time, reaching across 

 the gulf within, have lighted up the higher slopes of the great mountain- 

 wall on the farther or eastern side of the crater valley, making it re- 



Fig. 3. Sunrise on Clavius, Tycho, 

 Plato, Etc. 



