And now for a time let us turn attention from the lunar sky to the scenery of the lunar landscape. Let us, in imagination, take our stand high upon the eastern side of the rampart of one of the great craters. Height, it must be remarked, is more essential on the moon to command extent of view than upon the earth, for on account of the comparative smallness of the lunar sphere the dip of the horizon is very rapid. Such height, however, would be attained without great exercise of muscular power, since equal amounts of climbing energy would, from the smallness of lunar gravity, take a man six times as high on the moon as on the earth. Let us choose, for instance, the hill-side of Copernicus. The day begins by a sudden transition. The faint looming of objects under the united illumination of the half-full earth and the zodiacal light is the lunar precursor of day-break. Suddenly the highest mountain peaks receive the direct rays of a portion of the sun’s disc as it emerges from below the horizon. The brilliant lighting of these summits serves but to increase, by contrast, the prevailing darkness, for they seem to float like islands of light in a sea of gloom. At a rate of motion twenty-eight times slower than we are accustomed to, the light tardily creeps down the mountain-sides, and in the course of about twelve hours the whole of the circular rampart of the great crater below us, and towards the east, shines out in brilliant light, unsoftened by a trace of mountain-mist. But on the opposite side, looking into the crater, nothing but blackness is to be seen. As hour succeeds hour, the sunbeams reach peak after peak of the circular rampart in slow succession, till at length the circle is complete and the vast crater-rim, 50 miles in diameter, glistens like a silver-margined abyss of darkness. By-and-by, in the centre, appears a group of bright peaks or bosses. These are the now illuminated summits of the central cones, and the development of the great mountain cluster they form henceforth becomes an imposing feature of the scene. From our high standpoint, and looking backwards to the sunny side of our cosmorama, we glance over a vast region of the wildest volcanic desolation. Craters from five miles diameter downwards crowd together in countless numbers, so that the surface, as far as the eye can reach, looks veritably frothed over with them. Nearer the base of the rampart on which we stand, extensive mountain chains run to north and to south, casting long shadows towards us; and away to southward run several great chasms a mile wide and of appalling blackness and depth. Nearer still, almost beneath us, crag rises on crag and precipice upon precipice, mingled with craters and yawning pits, towering pinnacles of rock and piles of scoria and volcanic débris. But we behold no sign of existing or vestige of past organic life. No heaths or mosses soften the sharp edges and hard surfaces: no tints of cryptogamous or lichenous vegetation give a complexion of life to the hard fire-worn countenance of the scene. The whole landscape, as far as the eye can reach, is a realization of a fearful dream of desolation and lifelessness—not a dream of death, for that implies evidence of preexisting life, but a vision of a world upon which the light of life has never dawned.
PLATE XXII.
ASPECT OF AN ECLIPSE OF THE SUN BY THE EARTH, AS IT WOULD APPEAR AS SEEN FROM THE MOON.
Looking again, after some hours’ interval, into the great crateral amphitheatre, we see that the rays of the morning sun have crept down the distant side of the rampart, opposite to that on which we stand, and lighted up its vast landslipped terraces into a series of seeming hill-circles with all the rude and rugged features of a terrestrial mountain view, and none of the beauties save those of desolate grandeur. The plateau of the crater is half in shadow 10,000 feet below, with its grand group of cones, now fully in sight, rising from its centre. Although these last are twenty miles away and the base of the opposite rampart fully double that distance, we have no means of judging their remoteness, for in the absence of an atmosphere there can be no aërial perspective, and distant objects appear as brilliant and distinct as those which are close to the observer. Not the brightness only, but the various colours also of the distant objects are preserved in their full intensity; for colour we may fairly assume there must be. Mineral chlorates and sublimates will give vivid tints to certain parts of the landscape surface, and there must be all the more sombre colours which are common to mineral matters that have been subjected to fiery influence. All these tints will shine and glow with their greater or less intrinsic lustres, since they have not been deteriorated by atmospheric agencies, and far and near they will appear clear alike, since there is no aërial medium to veil them or tarnish their pristine brightness.
In the lunar landscape, in the line of sight, there are no means of estimating distances; only from an eminence, where the intervening ground can be seen, is it possible to realize magnitude in a lunar cosmorama and comprehend the dimensions of the objects it includes.
And with no air there can be no diffusion of light. As a consequence, no illumination reaches those parts of the scene which do not receive the direct solar rays, save the feeble amount reflected from contiguous illuminated objects, and a small quantity shed by the crescent earth. The shadows have an awful blackness. As we stand upon our chosen point of observation, we see on the lighted side of the rampart almost dazzling brightness, while beneath us, on the side away from the sun, there is a region many miles in area impenetrable to the sight, for there is no object within it receiving sufficient light to render it discernible; and all around us, far and near, there is the violent contrast between intense brightness of insolated parts and deep gloom of those in equally intense shadow. The black though starlit sky helps the violence of this contrast, for the bright mountains in the distance around us stand forth upon a background formed by the darkness of interplanetary space. The visible effects of these conditions must be in every sense unearthly and truly terrible. The hard, harsh glowing light and pitchy shadows; the absence of all the conditions that give tenderness to an earthly landscape; the black noonday sky, with the glaring sun ghastly in its brightness; the entire absence of vestiges of any life save that of the long since expired volcanoes—all these conspire to make up a scene of dreary, desolate grandeur that is scarcely conceivable by an earthly habitant, and that the description we have attempted but insufficiently pourtrays.
A legitimate extension of the imagination leads us to impressions of lunar conditions upon other senses than that of sight, to which we have hitherto confined our fancy. We are met at the outset with a difficulty in this extension; for it is impossible to conceive the sensations which the absence of an atmosphere would produce upon the most important of our bodily functions. If we would attempt the task we must conjure up feelings of suffocation, of which the thoughts are, however, too horrible to be dwelt upon; we must therefore maintain the delusion that we can exist without air, and attempt to realize some of the less discomforting effects of the absence of this medium. Most notable among these are the untempered heat of the direct solar rays, and the influence thereof upon the surface material upon which we suppose ourselves to stand. During a period of over three hundred hours the sun pours down his beams with unmitigated ferocity upon a soil never sheltered by a cloud or cooled by a shower, till that soil is heated, as we have shown, to a temperature equal nearly to that of melting lead; and this scorching influence is felt by everything upon which the sun shines on the lunar globe. But while regions directly insolated are thus heated, those parts turned from the sun would remain intensely cold, and that scorching in sunshine and freezing in shade with which mountaineers on the earth are familiar would be experienced in a terribly exaggerated degree. Among the consequences, already alluded to, of the alternations of temperature to which the moon’s crust is thus exposed, are doubtless more or less considerable expansions and contractions of the surface material, and we may conceive that a cracking and crumbling of the more brittle constituents would ensue, together with a grating of contiguous but disconnected masses, and an occasional dislocation of them. We refer again to these phenomena to remark that if an atmospheric medium existed they would be attended with noisy manifestations. There are abundant causes for grating and crackling sounds, and such are the only sources of noise upon the moon, where there is no life to raise a hum, no wind to murmur, no ocean to boom and foam, and no brook to plash. Yet even these crust-cracking commotions, though they might be felt by the vibrations of the ground, would not manifest themselves audibly, for without air there can be no communication between the grating or cracking body and the nerves of hearing. Dead silence reigns on the moon: a thousand cannons might be fired and a thousand drums beaten upon that airless world, but no sound could come from them: lips might quiver and tongues essay to speak, but no action of theirs could break the utter silence of the lunar scene.
At a rate twenty-eight times slower than upon earth, the shadows shorten till the sun attains his meridian height, and then, from the tropical region upon which we have in imagination stood, nothing is to be seen on any side, save towards the black sky, but dazzling light. The relief of afternoon shadow comes but tardily, and the darkness drags its slow length along the valleys and creeps sluggishly up the mountain-sides till, in a hundred hours or more, the time of sunset approaches. This phenomenon is but daybreak reversed, and is unaccompanied by any of the gorgeous sky tints that make the kindred event so enrapturing on earth. The sun declines towards the dark horizon without losing one jot of its brilliancy, and darts the full intensity of its heat upon all it shines on to the last. Its disc touches the horizon, and in half an hour dips half-way beneath it, its intrinsic brightness and colour remaining unchanged. The brief interval of twilight occurs, as in the morning, when only a small chord of the disc is visible, and the long shadows now sharpen as the area of light that casts them decreases. For a while the zodiacal light vies with the earth-moon high in the heavens in illuminating the scene; but in a few hours this solar appendage passes out of view, and our world becomes the queen of the lunar night.
At this sunset time the earth, nearly in the zenith of us, will be at its half-illuminated phase, and even then it will shed more light than we receive upon the brightest of moonlight nights. As the night proceeds, the earth-phase will increase through the gibbous stages until at midnight it will be “full,” and our orb will be seen in its entire beauty. It will perform at least one of its twenty-four-hourly rotations during the time that it appears quite full, and the whole of its surface features will in that time pass before the lunar spectator’s eye. At times the northern pole will be turned towards our view, at times the southern; and its polar ice-caps will appear as bright white spots, marking its axis of rotation. If our lunar sojourn were prolonged we should observe the northern ice-cap creep downwards to lower latitudes (during our winter) and retreat again (during our summer); and this variation would be perceptible in a less degree at the southern pole, on account of the watery area surrounding it. The seas would appear (so far as can be inferred) of pale blue-green tint; the continents parti-coloured: and the tinted spots would vary with the changing terrestrial seasons, as these are indicated by the positions and magnitudes of the polar ice-caps. The permanent markings would be ever undergoing apparent modification by the variations of the white cloud-belts that encircle the terrestrial sphere. Of the nature of these variations meteorological science is not as yet in a position to speak: it would indeed be vastly to the benefit of that science if a view of the distribution of clouds and vapours over the earth’s surface, as comprehensive as that we are imagining, could really be obtained.
It might happen at “full-earth,” that a black spot with a fainter penumbral fringe would appear on one side of the illuminated disc and pass somewhat rapidly across it. This would occur when the moon passed exactly between the sun and the earth, and the shadow of the moon was cast upon the terrestrial disc. We need hardly say that these shadow-transits would occur upon those astronomically important occasions when an eclipse of the sun is beheld from the earth.