56 



♦ KNOWLEDGE ♦ 



[July 27, 1883. 



THE MOON IN A THREE-INCH 

 TELESCOPE. 



By a Fellow of the Royal Astronomical Society. 



ERATOSTHENES (110), of which we spoke on p. 391 

 of Vol. III. as terminating the magnificent chain of 

 the Lunar Appenines, presents a beautiful spectacle about 

 the ninth day of the moon's age. Our drawing was made 



Eratosthenes. Moon's Age, 9'23 days. 



■with a power of 160, when the moon's age was 9 -2 3 days. 

 The diameter of this finely-terraced formation is about 

 37i miles, and its walls will be seen to be very rugged. 

 The three central peaks, too, are conspicuously shown 

 under this illumination. It is curious that a formation 

 presenting such strongly-marked features when lighted 

 obliquely by the rising or setting sun, should be by no 

 means easy to find at full moon. South-east of Eratosthenes 

 will be noted a deep mountain range, terminating in a ring- 

 plain whose walls are only some 1 30 ft. or so high. Hence 

 it is only visible during a short period of favourable illu- 

 mination, and forms a very severe test of the defining 

 power of a 3-in. telescope, and of the keenness of the 

 observer's vision. The height of the connecting ridge of 

 mountains is some 4,470 ft. As Ben Nevis is 4,406 ft., and 

 Snowdon only 3,. 571 ft. high, this maysuffice to furnish a scale 

 whereby the student may estimate the dimensions of the lead- 

 ing features of this neighbourhood. Schruter (106), or rather 

 its northern vicinity, should be carefully looked at when 

 near to the terminator, for the strange .system of ramparts 

 sloping ofl' on either side of a central one, which Gruithuisen 

 believed to be artificial, but which in reality consists of a 

 series of parallel valleys. Parry (217), Bonpland (218), 

 and Era Mauro (219), are those more or less imperfect 

 ring-plains which present a curious appearance when pretty 

 near the terminator. Pitatus (186) and Hesiod (187) are 

 a pair of huge craters, or rather ring-plains, connected by 

 a pass. The northern wall of the former will be seen to 

 be imperfect, while the southern wall is separated from 

 Tycho, which we are immediately to examine, by a rugged 

 mass of mountain peaks. The two most notable pecu- 

 liarities in Hesiod are a central crater in the floor, and a 

 cleft (shown in our map) running into the Sea of Clouds. 

 And now we arrive at what has been aptly called by Mr. 

 Webb, " the metropolitan crater of the moon," Tycho (180), 

 reference to the system of streaks emanating from which 

 has been once or twice previously made. This splendid 

 formation, visible as a white spot to the naked eye at full 

 moon, measures fifty-four and a quarter miles across, and 

 xhibits an elaborately terraced wall, some 16,000 ft 

 high on the east side ar.d upwards of 17,000 ft. in 



height in its western portion. In the subjoined sketch 

 we have purposely abstained from any attempt to 



T}-cl)0. Moon's Age, 924 days. 



delineate the extremely disturbed and rugged region 

 surrounding Tycho, confining ourselves strictly to drawing 

 the crater itself. The central hill shown above is between 

 .^jOOO and 6,000 feet high, its conical shadow being very 

 conspicuous at the time our drawing was made. The inex- 

 tricable mass of craters, hillocks, pits, and irregularities in 

 the immediate neighbourhood of Tycho almost defies any 

 attempt to draw or map it. The wonderful system of light 

 rays radiating from this great crater extends over at least 

 a quarter of the entire visible hemisphere of the moon. 

 Some of them may be traced to the southern limb, and 

 doubtless extend beyond it into that hemisphere which is 

 always hidden from the terrestrial observer. Onetremendous 

 ray passes through the Sea of Serenity, the craters 70 and 

 73 in our Map (Vol. III., p. 223), lying upon it. Another 

 very conspicuous one connects Tycho with the interesting 

 formation Bullialdus (213). It is a notable fact that while 

 these rays in nearly every other instance pursue their 

 course tlirough hill, valley, crater, and plain without 

 deviation or interruption, the crater Saussure (196) 

 has deflected one of them, and caused it apparently to 

 bend round its southern wall. What these stupendous 

 bands are can only be regarded, at present, as a mystery. 

 Nasmy th considers them to be cracks filled up with molten 

 lava from the Moon's interior ; but arguing from their ter- 

 restrial analogues, trap-dykes, we should expect to find them 

 projecting more or less above parts of the lunar surface, 

 and, as a necessary consequence, casting shadows when on 

 or near the terminator. As a matter of fact, we find them, 

 everywhere, absolutely level with the regions which they 

 traverse. Of whatever material they are composed, its re- 

 flective power must be very high, inasmuch as the ray- 

 system of Tycho traverses the (in many cases) huge and 

 complicated formations, Sasserides (183), Gauricus (185), 

 Heinsius (190), Wilhelm I. (191), Longomontanus (192), 

 Clavius (193), Maginus (195), Orontius (197), Nasir-ed-din 

 (198), Lexell (199), Walter (200), Moretus (262), Stofler 

 (354), and Maurolycus (358), all which are most con- 

 spicuous oVijects when obliquely lighted ; but which, one 

 and all, disappear wholly at full moon, or under vertical 

 illumination ! The late Professor Nichol, amid much 

 which, after all, merely amounted to assertion, did point 

 out one valuable piece of evidence furnished by these 

 rays ; and that is, the proof afi'orded by their continuous 

 visibility and the homogeneous character of their brightness 

 throughout their course, that the reflective substance of 

 which they are composed is absolutely everywhere uncovered. 

 Did anything in the shape of vegetation, for example, exist 

 in the moon, it must obscure portions of these light 

 streaks. That they pass undimmed, then, from their 

 origin to their termination, shows plainly enough that they 

 traverse " a rocky desert, devoid of life or living thing." 

 Here our night's work may cease. We shall turn our 

 telescope upon Copernicus (112) as soon as it is favourably 

 illuminated. 



