THE MOON 61 



just reversed. The new Moon is longer above the 

 horizon in summer than in winter ; the full Moon is 

 longer above the horizon in winter than in summer. 



The Moon's face exhibits a pattern which is always 

 much the same, for the Moon turns the same face 

 towards the earth. There is, however, a belt about 

 the Moon, occupying about one-fifth of her surface, 

 which is sometimes visible from the earth and some- 

 times not. The pattern on the Moon was formerly 

 supposed to be due to continents and seas, but 

 telescopic examination shows that the Moon has 

 no water on her surface. More than this, she has 

 either no atmosphere at all, or an atmosphere very 

 much less dense than that of the Earth. When she 

 passes between us and a star, the star disappears 

 suddenly, instead of being lost in haze. No clouds 

 are even seen to hide the pattern of the Moon's 

 surface. 



The telescope reveals the cause of the peculiar 

 markings. Lord Rosse's great telescope magnifies 

 6,000 diameters, and should have the effect, apart 

 from disturbing causes, of showing us the Moon at a 

 distance of only thirty-nine miles. But no telescope 

 is optically perfect, and the earth's atmosphere greatly 

 interferes with clear vision. We do not get nearly so 

 good a view of the Moon as the magnifying power of 

 the largest telescopes would lead us to expect. The 

 patches and dots upon the Moon are resolved by a 

 good telescope into crater-like mountains, casting 

 very sharp shadows. Some of these craters are very 

 large. Tycho has a diameter of more than fifty miles, 

 and covers an area almost as large as the West Riding 



