140 



Marvels of the Universe 



others, then the uninterrupted succession of her phases and their exceeding regularity, all these 

 particularities attracted the special attention of the inhabitants of the earth to this mysterious 

 star. 



The result of a long period of thought was the conclusion that these phases were due to the 

 movement of the moon round the earth ; that the lunar sphere, our faithful satellite, did not possess 

 anj- hght of herself, and that the extent of her iUumination depended on the position she occupied 

 in relation to the sun, from whom she derived her light. When she is situated above the earth 

 and is in conjunction with the day-star — that is to say, in direct opposition to the sun — the half of 

 her sphere which is turned towards the earth receives the direct flood of the solar rays ; that is 



the period of the full moon. 

 \^'hen she is lit obliquely or at 

 right angles onlj^ a part of her 

 surface appears brilliant, which 

 varies according to the angle 

 at which the moon receives the 

 sun's rays. When the western 

 half of the disc is visible that 

 is the first quarter ; fifteen 

 days later the eastern half is in 

 its turn illumined, and that is 

 the last quarter. At the 

 moment when the moon passes 

 between the earth and the sun 

 she is totally invisible, because 

 the half of the sphere receiving 

 the light is directed towards 

 the greater luminary, and the 

 other half, which possesses no 

 light in its own nature, remains 

 too dark to be perceived. 

 That is the new moon. But 

 about two days after the con- 

 junction of the sun and the 

 moon the latter reappears to 

 the west in the beautiful guise 

 of a crescent delicately defined 

 as if it were a sickle of light suspended in the darkling sky of evening. Sometimes during 

 this phase the part of the sphere which is not directly lit is outlined in grey against the 

 background of the sky. This shadowed light is the reflection of the earth light — that is to say, 

 of the light of the sun reflected by the complete hemisphere of the earth and again reflected to us by 

 the lunar disc. Our satellite, the moon, takes twenty-seven days, seven hours, forty-three minutes, 

 eleven and a half seconds to reach the same position in the sky as regards its relation with the stars 

 and to accomplish what is termed the sideral revolution, but it is necessary for her to continue her 

 journey for about two days longer in order to come back to her position between the earth and the 

 sun, who, in the interval of lunar circuit, have been displaced, the first in very fact, by the move- 

 ment of the annual journe}', the second in appearance only, owing to an effect of perspective 

 resulting from the displacement of our globe, which brings the synodic revolution of the moon to 

 occupy a total period of twenty-nine days, twelve hours, forty-four minutes, three seconds ; and this 

 fact is of the utmost importance to us, for it determines the exact time of the moon's phases. 



Photo iy'] 



[C. F/aiiiiimrion. 



THE MOON'S SURFACE. 



I possess upon tKe Moon, towards tKe centre of the visible hemisphere, a property 

 of considerable dimensions, the Circle oi Flammarion, with a diameter of 33 miles." 



