The Moon. 193 



THE MOON. PLANETS OF THE MONTH. DOUBLE 

 STAR, OOCULTATIONS. 



BY THE REV. T. W. WEBB, M.A., F.R.A.S. 



INDEX-MAP OP THE MOON. 



The accompanying diagram of the moon is not intended as a 

 pictorial representation of the surface of our satellite, but as 

 a guide to the position of the more conspicuous spots or inte- 

 resting regions ; and beyond this it makes no pretensions.* 

 From the principle of selection which has been adopted, it is 

 hoped that it will be less perplexing to the amateur who is 

 commencing the study of our satellite, than if it were a 

 crowded reduction of a larger map ; and while it will assist 

 him in acquiring the nomenclature of the principal features, its 

 more express object will be to enable him to identify the posi- 

 tion of the details which it is intended to describe successively 

 in future papers. It has been divided into two halves, in 

 order to avoid the inconvenience of folding ; and bisection in 

 an E. and W. direction has been preferred to the more natural 

 one from N. to S., as interfering with much fewer objects. 

 This, however, has entailed the necessity of turning the 

 diagram on its side, that it may present an aspect similar to 

 that of the full moon in an inverting telescope. The grey 

 plains, or so-called seas, are distinguished by Roman capital 

 letters, the craters and mountains by Arabic numerals, corres- 

 ponding with the accompanying list, which, it will be observed, 

 has been so arranged as to bring the designation as nearly 

 opposite as may be to the spot to which it belongs. The great 

 work of Beer and Madler being adopted as the standard 

 authority, their order has been followed in the distribution of 

 the numbers, though its appropriateness may not be in every 

 instance as apparent as might be wished. The student is re- 

 commended to pay especial attention to the situation of the 

 points of the compass, which differs materially from that 

 recognized almost universally in terrestrial maps. Tho reason of 

 this peculiarity will be clear if the diagram is turned upside 

 down ; it will then represent the full moon as seen on the me- 

 ridian without a telescope, and the designation of each part of 

 the lunar disc will be found to correspond with the points of the 

 terrestrial compass on every side. This semi-inversion, which 

 arises from our standing face to face with the object, and 

 is exactly that of a common looking-glass, or a front-view 



* A much more complete map, twelve inches in diameter, containing every 

 spot included in the nomenclature of Beer and Madler (401 in all), will be found, 

 in the author's little work entitled Celestial Objects for Common Telescopes. 



