294 



♦ KNOWLEDGE ♦ 



(Mat 18, 1883. 



THE MOON IN A THllEB-INCH 

 TELESCOPE. 



By a Fellow of the Royal Astronomical Society. 



OUK first essay in the examination of the lunar surface 

 (p. 20")) was supposed to be made wlien the moon 

 was between three and four days old. To night we will 

 imagine that her age has increased, and is about six days. 

 The first thing which will strike the attentive student is 

 the changed aspect, under the more vertical light of the 

 sun, of the formations he has observed at an earlier date 

 in the lunation. Objects near the moon's western limb, 

 which, lit laterally by the rising sun, cast black shadows, 

 and so revealed their configurations distinctly, are now 

 illuminated (like the " depths of the sea," in the famous 

 prize poem) by "the sun's perpendicular rays," and are 

 converted into mere bright blotches upon a darker back- 

 ground. A strange formation, which was close to the ter- 

 minator at the epoch of our last observation, so curiously 

 illustrates the change of aspect induced by varying illumi- 

 nation, that we give three illustrations of it as seen in the 

 waxing, full, and waning moon at the ages given under the 

 respective drawings. It is numbered 327 in our Map, on 



ier. Moon's Age, 17'8 days. 



p. 223, and is called Messier, presumably from its resem- 

 blance to a comet ; the French astronomer, after whom it 

 is named, having been, as is pretty well known, one of the 

 keenest searchers for and discoverers of comets of the last 

 century. 



Messier. Moon's Age, 3"95 days. 



Messier. Fnll Jloon. 



The two slightly diverging streaks which seem to radiate 

 from the right hand, or eastern, of the two craters 

 (" Messier A"), appear almost artificial in their regularity. 

 The most curious thing, however, in connection with these 

 two craters is thi.s : that Miidler, as the result of a large 

 number of observations, called pointed attention to their 

 precise similarity in size, form, depth, and brightness. A 

 glance at either of our drawings made at the telescope at 

 the epochs specified will suffice to show that they now differ 

 widely in this respect : that Messier itself (the western 

 one) is decidedly smaller than Messier A, and that their 

 major axes lie approximately at right angles to each other. 

 The young observer should try to view this formation 

 under the same illumination as we ourselves did in making 

 the third of the aViove sketches ; the long peaked shadows 

 revealing curiously the structure of the crater walls which 

 cast them. Messier itself is about nine miles in diameter. 

 The southern extremity of the Sea of Nectar (V) termi- 

 nates in a kind of bay, known as Fracastorius (372). 



Under this illumination Fracastorius looks like what we 

 have called above a bay. If, however, it be observed 

 when quite close to the terminator (preferably in the 

 waning moon), it will be seen as a complete circle, the 

 northern part of it consisting of low detached blocks. 

 South of it is a very fine object, the grand ring-plain Pic- 

 colomini (371), about 57 i miles in diameter. Between this 



and Fracastorius the moon is very mountainous. South of 

 Piccolomini lie a number of craters and ring-plains, whoso 



Fracastorius. Moon's Age 5'65 days. 



names may be learned from our map. Starting now from 

 the north side of the Sea of Nectar we find an interesting 

 pair of craters, Isidore and Capella (323 and 324) ; and 

 crossing the Sea of Tranquillity from south to north we 

 arrive at a groiip of craters, Rijmer (52), Littrow (55), 

 Maraldi (56), and Vitruvius (57). A little range of moun- 

 tains of the ordinary terrestrial type, called Mount Arg»us. 

 (58), will be noted just on the Sea of Tranquillity. On the 

 north-west boundary of the Sea of Serenity (H) lies one 

 of the largest ring-plains in the moon, Posidonius (5-t), 

 some G2 miles in diameter. There is a fine central crater 

 in this formation, and it would form an instructive- 

 exercise for the incipient selenographer who can draw,. 

 to try and sketch some of the details which abound in 

 this fine object. Atlas (28) and Hercules (29) here drawri 



Atlas and Hercules. Moon's Age, o'Co days. 



are two noble walled plains or depressions, 55 miles and 

 46 miles broad respectively. It will be noted that while 

 the most conspicuous object in the interior of Atlas is a 

 mountain, in Hercules it is a crater. Glancing at Pliny (61), 

 a fine terraced ring, full of little hills, on our way south- 

 ward again, we will conclude our night's work by the- 

 examination of that noble triple group, Tlieophilus, CyriUus, 

 and Catherine (319, 320, 321). The study of the connec- 

 tion between these grand objects and of the way in which 

 they are connected supplies us with a key to the chronology 



Catherine, Cyrillus, and Tlieophilus. Moon's Age, 5'C5 days. 



of this part of the lunar surface. The valley connecting 

 Catherine and Cyrillus will be observed, as also the way 



