Fig. 72.—The Lunar Apennines.
The absence of sensible atmosphere must produce an effect on the temperature of the Moon analogous to that perceived on the high mountains of our globe, where the rarefaction of the air does not permit the solar heat to concentrate itself upon the surface of the soil, as it does below the atmosphere, which acts as a forcing-house: the Sun's heat is not kept in by anything, and incessantly radiates out toward space. In all probability the cold is extremely and constantly rigorous, not only during the nights, which are fifteen times longer than our own, but even during the long days of sunshine.
We give two different drawings to represent these curious aspects of lunar topography. The first (Fig. 72) is taken in the neighborhood of the Apennines, and shows a long chain of mountains beneath which are three deep rings, Archimedes, Aristillus, and Autolycus: the second (Fig. 73) depicts the lunar ring of Flammarion,[14] whose outline is constructed of dismantled ramparts, and whose depths are sprinkled with little craters. The first of these two drawings was made in England by Nasmyth, the second in Germany by Krieger: they both give an exact idea of what one sees in the telescope with different modes of solar illumination.
In the Moon's always black and starry sky a majestic star that is not visible from the Earth, and exhibits this peculiarity that it is stationary in the Heavens, while all the others pass behind it, may constantly be admired, by day as well as by night; and it is also of considerable apparent magnitude. This orb, some four times as large as the Moon in diameter, and thirteen to fourteen times more extensive in surface, is our Earth, which presents to the Moon a sequence of phases similar to those which our satellite presents to us, but in the inverse direction. At the moment of New Moon, the Sun fully illuminates the terrestrial hemisphere turned toward our satellite, and we get "Full Earth"; at the time of Full Moon, on the contrary, the non-illuminated hemisphere of the Earth is turned toward the satellite, and we get "New Earth": when the Moon shows us first quarter, the Earth is in last quarter, and so on. The drawing subjoined gives an idea of these aspects.
Fig. 73.—Flammarion's Lunar Ring.
What a curious sight our globe must be during this long night of fourteen times twenty-four hours! Independent of its phases, which bring it from first quarter to full earth for the middle of the night, and from full earth to last quarter for sunrise, how interested we should be to see it thus stationary in the sky, and turning on itself in twenty-four hours.