Part 21

THE GIANT RING MOUNTAINS, THEOPHILUS AND ITS NEIGHBORS. ]

“Yes,” I assented, “it surely is terrible here. In a little while, however, I shall show you a lunar scene of surpassing beauty. But study this spectacle with an inquiring mind and you will find that it, too, has its attractions. You are now looking upon Theophilus, Cyrillus, Catharina, and the surrounding region as the astronomer sees them with the most powerful telescopes. Indeed, with the telescope he sees the details more sharply than they are visible here, for the best photographs still lack something in distinctness. The illumination when this picture was taken was practically the same as in the last that we examined, but the magnification is much greater. Look, now, at the central mountain in Theophilus. Its great buttresses cast their shadows into profound ravines and chasms, imparting to it a most singular outline. Observe the tooth-shaped shadows of its two principal peaks, thrown westward across the floor, while the broad shadow of the western wall emphasizes the immense depth of the depression. The glare of the afternoon sun on the cliffs of the inner side of the eastern wall is so brilliant that the details are obscured. But the surface of the moon outside, particularly toward the north and the west, is beautifully brought out with all its wonderful modulations and irregularities. Judging by appearances, those who hold that Theophilus and similar formations, notwithstanding their enormous magnitude, are really of volcanic origin, have the strongest reasons for their opinions. Immense flows of lava seem to have taken place on all sides of the great ring, entering the Mare Nectaris on the west. Notice the huge mountain fold which runs from the parallel ridges on the southwestern side of Theophilus to the crater ring Beaumont, lying west of Catharina. Observe, also, the complicated form of the wall dividing Theophilus and Cyrillus. Two deep ravines, shown by the shadows that fill them, cross one another like the arms of a flat letter X. One of these ravines turns northward along the wall and re-enters Theophilus, while the other continues for a long distance within the western side of Cyrillus. I cannot imagine a more interesting or a more stupendous excursion for a geologist, a mountaineer, or a seeker after wonderful and sublime aspects of nature, than a climb around the crest of the wall of Theophilus—if indeed such a climb can be regarded as humanly possible.

“Now, again, I am reminded of what I once told you about the amazing contrasts of light and darkness, and of heat and cold, upon the moon. Suppose yourself standing on the verge of the eastern wall of Theophilus where the edge seems sharpest, and looking down into the abyss at your feet. The sun’s rays would be unbearably hot where they touched your face and hands, but if you let yourself down a little way into the blackness beneath you would not only pass instantly into night, but you would shiver and shrink with cold so frightful that no winter experience that you have ever had could give an idea of its intensity. From that point of observation you would look across a chasm of inky darkness, 25 miles broad, and see, towering up from the illuminated plain afar off, with their summits more than two miles below your level, the brilliant group of the central peaks, while behind them the crest of the western wall would appear like a bright line on the horizon 60 miles away. Changing your place to one of the peaks on the dividing wall you would look down into Theophilus on one side and Cyrillus on the other. Then upon lifting your eyes to the black, airless sky you would see the stars sparkling on all hands, and, hanging in the heavens like a portentous, strangely colored moon many times larger than the disk of the sun, would appear the mottled orb of the earth. The terrific nature of the scenery around you, the meeting of day and night at your feet, and the incredible blending together of their characteristic aspects in the sky above you, the startling magnitude of the suspended earth—all these things combined would make you feel as if you were not only in another world but in another universe.”

“I no longer wish to visit the moon,” interrupted my friend, shaking her head.

“Not if you were assured of a safe return?”

“No, it would upset my mind. I am certain that I should go crazy in such a world where everything seems to be topsy-turvy.”

“Wait until we arrive at the ‘Sea of Serenity’ once more, and perhaps you will think better of it. Notwithstanding the increased magnification, the details in Cyrillus and Catharina are hardly better seen in this photograph than in its predecessor, but the increase of size is very effective in emphasizing some of the features of the surrounding district. Cyrillus is seen to have a decided hexagonal outline, and west of its southern corner is an exceedingly curious formation, approaching closely to a square shape. The wall is illuminated within on all four sides, and out of the midst of the lozenge-shaped shadow resting over the bottom of the included valley, rises a mountain which, like the walls, is bright with sunshine. On the southwest a semicircular ridge runs out into the darkness, its top brightly illuminated. The general effect of the entire formation is fantastic. And could you imagine a wilder scene than that presented by the elongated mountain mass, which starts from the southwestern side of Cyrillus, skirts the border of Catharina, and continues on along the northwestern side of the broad valley in the upper part of the picture? See how it has, apparently, been rent apart by tremendous forces and torn by volcanic outbursts, which have left yawning craters everywhere. Even the valley itself seems to be simply a chain of wrecked crater rings of vast size, the cross walls having nearly disappeared. Observe, too, the immense number of crater pits of all sizes scattered everywhere, both inside the ring plains (Theophilus alone having few of them) and over the surrounding country. We shall see a still more remarkable example of this pitting of the lunar surface in the neighborhood of Copernicus, which is the chief object in the next photograph that we take up.”

We came now to the large picture of Copernicus, and my friend took it in her hands to examine it.

“It is a marvelous thing to look upon,” she said, “but it doesn’t frighten me as Theophilus did.”

“No, Copernicus is rather sublime than terrifying in aspect. Its comparatively lone situation, with the Mare Nubium, the Oceanus Procellarum and the Mare Imbrium surrounding it on all sides with their broad, level expanses, gives it an appearance of solitary grandeur belonging to no other single formation on the moon. ‘The monarch of the lunar ring mountains,’ Mr. Elger has termed it. First let me tell you the principal facts known about Copernicus. It is 56 miles in diameter, two miles more than Tycho, and eight less than Theophilus. It is not as deep as either of those formations, the highest points on its walls being 12,000 feet. But the walls are more uniform in height than is usual with so extensive a ring. They are very steep on the inside, especially near the top, where their slope has been estimated by Neison at from 50° to 60°. To a person standing on their verge they would seem almost perpendicular. The central mountain consists of five principal peaks. The outer slopes of the ring are also steep, but its maximum height above the surrounding surface does not exceed 3,000 or 4,000 feet, so that Copernicus, like the other great ring mountains, is, in reality, a vast sink, encircled with a mountain ridge. You will note that Copernicus clearly exhibits the tendency to a hexagonal form which we have observed elsewhere, although it stands alone with no other great rings pressing against its walls. Curiously enough the form of Copernicus is very closely repeated in the small crater ring Gay Lussac, situated in the mountains on the lower (north) side. This picture, I should remark, unlike the last two preceding it, was taken near lunar sunrise, and accordingly the light comes from the west. This is the best illumination for studying Copernicus and its vicinity. Of all the great ring plains Copernicus perhaps gives the most striking testimony in favor of the view of those who hold that the lunar volcanoes were once the actual centers of volcanic action, resembling the volcanoes of the earth in the ejection of vapors, ashes, stones, and streams of lava. The slopes around Copernicus for many miles look as though they had been covered with lava and pitted with minor craters such as appear on the shoulders and in the vicinity of many of our volcanoes, while the appearance of the great ring does not contradict the theory of Nasmyth and Carpenter, which I have previously mentioned, that it was built up by ejections from a central crater now more or less completely filled. As I have already told you the lunar volcanoes differ essentially from those of the earth in that their central depressions lie deep beneath the level of the surrounding surface of the moon. This is strikingly true of Copernicus, and it is a result that might have been foreseen from the enormous size of the craters. A mountain of sufficient magnitude to carry the vast cup of Copernicus on its head, as Vesuvius, Etna, Cotopaxi, and Popocatepetl carry their craters, could not stand even on the moon. Observe the generally radial arrangement of the lines about Copernicus, recalling the similar arrangement of lava flows about terrestrial volcanoes. Some of these lines, as you will see, consist of long rows of pits. Similar phenomena may be seen along the lava streams that we are familiar with on our planet, where small craters break forth one after another. A striking example of this arrangement is visible in the photograph on the northeastern slope leading up toward the Copernicus ring. But you will also see many very remarkable rows of pits in the vicinity of Copernicus which are not radial in arrangement with respect to the ring. The most conspicuous of these is on the northwestern side, about half way between Copernicus and the ring of Eratosthenes, which standing at the upper end of the chain of the Apennines appears at the left-hand edge of the picture. There are hundreds, probably thousands, of these pits on all sides of Copernicus.

“One of the explanations that has been suggested for them is that they were produced by the fall of enormous volcanic bombs thrown from Copernicus when it was in eruption. I wish merely to mention this idea without comment. It however calls up another interesting theory, which has not met with much acceptance, to the effect that such lunar volcanoes as Copernicus may have been powerful enough to eject masses of lava and rocks with a velocity sufficient to enable them to escape from the attraction of the moon, whereupon they became meteorites traveling in independent orbits around the sun. Some of these, the theory suggests, may be among those that have fallen upon the earth. A velocity of a mile and a half per second would be sufficient to overcome the gravitation of the moon. That is only three or four times the initial velocity which some modern guns are capable of imparting to their projectiles.”

“I am sorry,” explained my friend, “that you seem to attach little importance to so interesting a theory. It stirs my imagination to think of the moon sending bits of herself back to her mother planet. For my part, the theory does not seem to be any harder to believe than that of your Professor Darwin that the whole moon was thrown off from the earth. Besides, it intensifies my appreciation of the grandeur of Copernicus when I am told that that great volcano could once bombard the earth across—what is it, 240,000 miles?—of space.”

“As you always choose the most picturesque theories to rest your belief upon, I shall not complain if you accept the lunar volcano theory of meteorites,” I replied. “But, for the present, we have done with it, and I am now going to ask you to inspect the photograph for other interesting objects. East and north of the great ring you will see an extensive mass of mountains. Those on the north, with immense buttresses projecting into the Mare Imbrium, are the lunar Carpathians. I have already directed your attention to a comparatively small crater ring which resembles a reduced copy of Copernicus, situated in these mountains at the head of a bay which penetrates southward between high ridges, for about 30 miles. This crater is named Gay Lussac. It has a small deep neighbor on the southwest. West of Gay Lussac the Carpathians gradually dwindle away until they sink to the level of the plain. Toward the east they project in several bold headlands, terminating with towering peaks into the ‘sea.’ Lying off the point of the headland on the western side of the bay that leads to Gay Lussac you will perceive two charming little craters, almost perfect twins. Much farther toward the north and west is a larger crater, more than half of whose interior is black with shadow. This is Pytheas. Its lonely situation is very striking, but upon close inspection you will notice that a low range of hills appears to connect it with the twin craters that I have just pointed out. This range of hills, lying on the ‘sea’ bottom, is curiously forked, the other branch leading to a pair of small peaks in the ‘sea,’ which possess no craters. The little crater east of Pytheas is also a beautiful object in the picture.

“Near the eastern end of the Carpathians the mountains make their greatest advance into the Mare Imbrium, leaving a large square-cornered bay on the west. From this point they turn southward, forming a complicated mass of peaks and ridges interspersed with craters and pits. These mountains east of Copernicus are among the most singular upon the moon, for they inclose a group of irregular-shaped plains, the walls of which consist of immense, more or less separate, masses. Look at the one nearest to Copernicus, which has somewhat the form of a starfish, and observe how curiously its southern border reflects, on a smaller scale, the forms characteristic of the headlands and bays along the shore of the Mare Imbrium below.

“Above Copernicus you see a large crater ring more than half in shadow, with a plain of an irregular hexagonal shape, northwest of it. The large ring is named Reinhold. A broken mass of mountains extends from its southern side far into the Mare Nubium. In the upper right-hand corner of the picture is another large ring called Landsberg. In the upper left-hand corner you see a roughly hexagonal ring plain, level on the interior, named Gambart. Mountains break the level of the mare both south and north of Gambart. Those on the north are remarkable for the darkness of the surface, especially in the northwestern part.

“Almost directly west of Copernicus lies an exceedingly singular object. It is a part of the underworld of the moon, the buried moon, which was covered up ages ago by that immense outgush of lava of which I have so often spoken. Once evidently it was a ring larger than Eratosthenes. Now, only its outlines can be traced, the whole immense depression of the interior and the surrounding walls to their very top having been covered up. It is pitted and surrounded with little craters of a later date. I have already told you that Eratosthenes, the ring at the left-hand edge of the photograph, marks the termination of the great range of the lunar Apennines. But these mountains seem to be continued beyond Eratosthenes in two short branches, one turning eastward toward the Carpathians, and the other reaching to the highest part of the buried wall of the submerged ring that we have been talking about and which bears the name of Stadius. You will be interested in knowing that southwest of Stadius, but off the edge of the picture, there is a place in which low hills and ridges abound, where the German astronomer Schröter imagined that he had discovered a lunar city! His mistake was, perhaps, natural, considering the slight power of his telescope and the strangely regular arrangement of the lines of hills which he mistook for streets.”

“I regret that he was deceived.”

TWO GREAT LUNAR “SEAS” The Mare Serenitatis and a Part of the Mare Imbrium. ]

“So do I. We shall now leave Copernicus and its marvelous surroundings, and turn to the last photograph in our series, representing the Mare Serenitatis in its full extent, and a large part of the Mare Imbrium. Is it not a beautiful picture?”

“It is, indeed, but so strange!”

“There is, I believe, nothing in the lunar world that would not seem strange to our eyes. To understand just what this picture means you should imagine yourself floating in an airship at an immense height above the surface of the moon. The Mare Serenitatis you will recognize as the great oval plain occupying the upper left-hand part of the photograph. It is entirely encircled by mountains except in three places—at its eastern end, where a broad strait opens between the Apennines on the south and the Caucasus on the north, leading into the Mare Imbrium; on the northwest, where another strait opens into the Lacus Somniorum, the ‘Lake of the Sleepers,’ or ‘The Dreamers,’ and on the southwest, where a third strait with a conspicuous crater in its center leads into the Mare Tranquillitatis. The Mare Serenitatis is 430 miles long and nearly as broad, and covers an area of about 125,000 square miles. A great many details are visible on its floor. Even if it were covered with water we might see these, for, as you have probably heard, the bottom of deep lakes is visible when one looks down upon them from a great height. The surface of water, however, at certain angles of view and of illumination, would produce flashes and glares of light which are never seen on this vast lunar plain.”

“Oh, but it must once have been a sea,” said my friend, poring over the photograph. “I cannot give up that idea. It gives the interest of life to the moon, if not now at least in the past.”

“You are by no means compelled to give up your idea,” I replied. “On the contrary you are supported by the opinion of many astronomers, including Messrs. Loewy and Puiseux, whom I quoted a little while ago. They aver that the resemblances between the lunar mares and the beds of our terrestrial oceans are too numerous and too decided to permit any other conclusion than that in the one case as in the other a deep covering of water has produced the characteristic features. One striking resemblance that they note is in the surface contours. The lunar sea beds are generally deepest along the shores; the same is true of the terrestrial seas. Continents on the other hand are characterized by concave surfaces. But before we study the two lunar ‘seas’ in detail let us first look at their shores and surroundings. The upper and right-hand sides of the Mare Serenitatis are bordered by hundreds of miles of magnificent cliffs, which in many places are very steep and of great height. These form what we may call the sea front of the Hæmus Mountains, which join the lunar Apennines on the southern shore of the strait leading into the Mare Imbrium. These mountains possess one conspicuous crater, set like a gem in the chain, at about a third of its length from the western end. This crater is Menelaus, which we saw in one of the smaller photographs. It is characterized by its exceptional brilliance as well as by the fact that the longest of the bright bands that start from Tycho passes through it, and then continues on across the Mare Serenitatis and the Lacus Somniorum, to the Mare Frigoris. This band, more than 2,000 miles long, has come all the way from Tycho, high in the southern hemisphere, never turning aside to avoid anything in its path. Mountains, craters, and ring plains are equally indifferent to it. It is like a Roman road, and like that, too, it suggests for its creation a power that knew no master, and admitted of neither rivalry nor opposition. The existence of this mysterious band increases the difficulty of finding a satisfactory explanation of the Tychonic rays. In the midst of the mare the band or ray crosses another lone crater, 14 miles in diameter, named Bessel. The full length of the ray is not shown in this photograph, but on its way from Bessel it touches two other small craters in the ‘sea.’

“That portion of the Hæmus range in which Menelaus is set is a very attractive scene on account of the bow shape of the mountains, and the situation of the bright crater just in the center of the bow. Menelaus and the streak from Tycho can be seen at Full Moon with no greater optical aid than that of a good binocular. On the edge of the ‘sea,’ off a lofty headland of the Hæmus chain, another lone little crater is visible, Sulpicius Gallus by name. It, too, is remarkable for its brilliant reflective power. Behind the mountains, directly back of Sulpicius Gallus, and lying in an upraised part of the Mare Vaporum, is a larger, and even brighter, crater ring than Menelaus. It is named Manilius, and is likewise a conspicuous object for a binocular at Full Moon. Below Sulpicius Gallus the Hæmus Mountains broaden out and assume a curious somber tone, until, in the form of a rough plateau, they blend with the wide-expanded southwestern slopes of the Apennines. The latter rise gradually to the chain of huge peaks fronting the Mare Imbrium. They contain one notable crater ring named Marco Polo, which lies just above a great square massif, which breaks the narrow chain of the illuminated summits of the Apennines. The precipitous front of this range appears very brilliant in the afternoon sun, for here again we have a photograph made after the time of Full Moon. The end of the Apennines touching the strait, of which I have previously spoken, terminates with a high cape called Mount Hadley. In the strait, off this cape, is an array of small mountain peaks, which must have been islands, if the lunar ‘seas’ were once true seas.

“Across the strait, on the northern side, stand the lunar Caucasus Mountains. They run out to a point in a long, irregular, broken ridge. The distance from Mount Hadley across the strait to the projecting point of the Caucasus range is about 50 miles. The islands narrow the main opening to a width of 30 miles. In strict fact the Caucasus range is not continuous. The point fronting the strait is, in reality, the end of a large irregular ‘island,’ with intricate channels separating it from the mainland. Still farther north the photograph shows a broad valley severing the mountain range from side to side. The main mass of the Caucasus continues northward to the great ring mountains Eudoxus and Aristoteles. In the center of the range, opposite the lower corner of the Mare Serenitatis, is an irregular ring plain, Calippus. West of this the mountains break down in great precipices to the level of a plain that might be compared with one of the ‘parks’ of Colorado. Beyond this, in the shape of a broad mass of hills, it skirts the border of the Mare Serenitatis for nearly 200 miles to a sharp promontory which shuts off the Lacus Somniorum on one side from the mare. West of Aristoteles and Eudoxus the mountain mass extends to a curious sharp-angled plain, which it skirts on the north and south.

“The western shore of the Mare Serenitatis beyond the strait opening into the Lacus Somniorum is bordered by a series of alternating ring plains and connecting mountains. The first and largest of the rings is Posidonius, an immense formation 62 miles in diameter, with a central crater and curious ridges within the inclosure. Above Posidonius is Le Monnier, a ring plain whose ‘seaward’ wall has been broken down. Above that, again, is a mountain range terminating with broken crater rings. Then we arrive at the strait opening into the Mare Tranquillitatis, which is twice as broad as that between the Apennines and the Caucasus, and just in the middle of it stands a very perfect crater ring named Dawes. On the eastern side of this strait the Hæmus Mountains begin with a long cape called the Promontory Acherusia. Above this promontory, at the edge of the picture, appears the ring plain Plinius, with a distinct central peak. This completes the circuit of the Mare Serenitatis.

“We return to the Caucasus region. These mountains front the Mare Imbrium along the upper part of their course with sharp slopes and cliffs. In the ‘sea,’ nearly opposite the deep, broad valley which I pointed out as dividing the range completely across, stands a triangular-shaped ring plain dark with shadow on one of its sides. This is Theætetus, interesting as the scene of an alleged display of ‘smoke,’ reported to have been witnessed by a French observer with his telescope a few years ago. Several occurrences of this kind have been reported on the moon, but more or less doubt attaches in every instance the accuracy of the observations, or at least to that of the conclusions drawn from them. Below Theætetus is an oval ring almost entirely filled up, with two craters within it. This is named Cassini. Below Cassini begins another mass of mountains, the lunar Alps. These are by no means as extensive as the Caucasus, but they contain some lofty peaks, and are traversed by one of the most remarkable valleys on the moon. It is not very distinctly shown in this picture, but you may recognize it by a dark band commencing opposite a small bay which sets back into the mountains. The valley continues through the mountains and the adjoining hilly regions nearly to the shore of the narrow Mare Frigoris, which runs in a sloping direction from beyond Aristoteles to the bottom edge of the picture. The Alps spread eastward, broadening out with many separate peaks, and skirting the Mare Imbrium, until they reach one of the most singular and interesting of lunar formations, the oval ring plain Plato. This looks like a dark lake surrounded by high cliffs. In the photograph all of the encircling wall is illuminated on the inner side except at the east end, where the shadows extend a short distance upon the floor. Plato looks as though it might once have been a ring mountain of the usual type, which has been partly filled in the interior by a local uprush of molten lava. The diameter of the ring is 60 miles, but the inclosure sinks only about half as deep beneath the crest of the wall, as is the rule with formations of similar outline. A central peak, a group of mountains, may be buried there.

“It is within this ring of Plato that some of the strongest evidences of continued change, and possibly of continued life upon the moon, have been found. Prof. William H. Pickering, after long and careful studies of this remarkable plain, says of it: