Part 6

NO. 7. JULY 2, 1903; MOON’S AGE 7.24 DAYS. ]

“Pardon me,” said my friend, “but it was not of names like those that I was thinking. Observe how he who named the neighboring _Palus Somnii_, ‘Marsh of a Dream,’ exhibited an exquisite delicacy of fancy. It suggests something indefinitely strange, romantic, imaginative. That unknown astronomer, unknown at least to me, put a little of himself, a little of his inmost mind, into the name, and I thank him for it. I shall never forget the ‘Marsh of a Dream’ in the moon. It will haunt my own dreams. I shall be all my life seeking and never finding its meaning.”

“Since you are in so poetic a mood,” I responded, “I rejoice that besides its bald facts, its fireless volcanoes, and its dried-up plains, the moon possesses many things that can stir the imagination of the most sentimental observer. But, in order that we may not wander too far from the paths of science, let me recall your attention to the photograph. We have been going over ground already trodden by returning to the neighborhood of the _Mare Crisium_. I shall now lead you back to the terminator, where we shall find a little that is new. Still nearly hidden in night we perceive many great rings on which the sun is beginning to rise, and four of the most important ranges of mountains are coming into view. One of these, on the southern border of the _Mare Serenitatis_, is visible throughout its entire extent. It forms a portion of the coquettish ornaments with which the Moon Maiden has decorated her hair, as we shall see clearly in the next photograph. This range is named the Hæmus mountains. Near its center, quite at the edge of the ‘sea,’ is a bright crater ring, one of the most conspicuous on the moon. It is called Menelaus.”

“Menelaus?” exclaimed my friend. “Ah, then Riccioli did not confine his favoritism to the astronomers and philosophers in putting their names in the moon. Menelaus, if I remember my classical reading correctly, was the husband of Helen of Troy.”

“Yes, the brother of Agamemnon himself. You must admit that Riccioli occasionally felt his imagination a little awakened. He was not altogether destitute of the spirit of poetry.”

“But did he also put Helen in the moon?”

“I am sorry to say that he did not. It would have been a very suitable abode for her. However, if you like, you may recognize Helen in the Moon Maiden herself.”

“Thank you, that will be, indeed, an unexpected pleasure.”

“Meanwhile allow me to point out to you that there is a curious light streak, very faintly shown in the photograph, which crosses the _Mare Serenitatis_ from Menelaus to the opposite shore, and reappears more distinctly, on the lighter-colored plain toward the north. This streak comes all the way from a great ring mountain named Tycho in the southern part of the moon. It is more than 2,000 miles long, and is one of the greatest mysteries of the lunar world. Tycho, which lies just on the sunrise line, is not well seen in this photograph. It has a great number of these strange streaks or rays proceeding from it in all directions. We shall study them in one of the photographs which are to come. One word in regard to the plain north of the _Mare Serenitatis_ of which I have just spoken. It, too, has a name that is calculated to appeal to your lively imagination. It is called the _Lacus Somniorum_, which if my knowledge of Latin is correct, means ‘Lake of the Sleepers.’”

“Then your old friend Riccioli certainly did not bestow the appellation.”

“No, it was one of his more fanciful, or, if you prefer, more poetical predecessors, perhaps the same who imagined the ‘Marsh of a Dream.’”

“Oh, that gives me another reason to think of him with admiration and gratitude. He, at least, had a soul that rose above mere prosaic facts.”

“Perhaps. But do not think too lightly of the facts of the moon. After all the human mind must base itself upon the solid ground of fact. Without that we should become mere dreamers, and be suited only to inhabit your favorite ‘Marsh.’”

“The other mountain ranges of which I have spoken,” I continued, “are faintly distinguishable eastward from the _Mare Serenitatis_. They are the Apennines, the Caucasus, and the Alps. But perhaps we had better turn at once to photograph No. 8 where they are much more clearly seen, because the sunrise there has advanced a couple of hundred miles farther east.”

“But, dear me, how slowly the sun rises on the moon! Was this photograph taken a day later than the other?”

“Almost exactly two days later. When it was made the moon was nearly nine and a quarter days old, and its age at the time No. 7 was made was only seven and a quarter days. But, owing to the effects of libration, an explanation of which I have put into a note for your private reading when you feel like it, [see p. 57, footnote], the difference of phase amounts to less than two days. You are right, however, in remarking that sunrise is a very slow process on the moon. It requires about two weeks to pass from the western side of the moon to the eastern side, and both day and night at any point on the moon last about a fortnight. This results from the fact that, as I have told you, the moon does not turn rapidly on its axis like our own globe, but keeps always the same side directed toward the earth. Accordingly, a lunar day and night are together about a month long.”

“And was it so when, as I must persist in believing, there were inhabitants on the moon?”

“Probably, although it may have been shorter then. The consequences of these excessively long days and nights would be very serious to beings fashioned upon the terrestrial plan. In the practical absence of an atmosphere the heat of the sun’s rays, pouring down without interruption and without the intervention of any clouds or vapors for fourteen days at a time, must be simply overpowering. And then, during the equally long night that ensues, the radiation into open space must quickly leave the surface of the moon exposed to the most frightful degree of cold, comparable with the absolute zero of empty space!”

“But think, what a merciless environment you are picturing for my inhabitants of the moon. Please do not forget that I insist that their comfort shall be considered.”

“Oh, as for that, you know you were content a little while ago to relegate your inhabitants to a remote period in the past, after the volcanic fury of the lunar world had ceased, and before its present airless and waterless condition had supervened. Possibly at that time things were not so uncomfortable for them. They may have had clouds to temper the sunshine, rains to cool the days and dews the nights, and shady parks like yours for philosophic and scientific contemplation.”

“Do not forget the poets.”

“Certainly not. But is not the moon herself the very spirit of poetry? What in nature is more poetical in its suggestions than the moon wading through fleecy clouds on a serene summer’s night? But pardon me, we are forgetting my mountains, upon which I insist as strongly as you do upon your inhabitants. The mountains have this advantage that they are very real, and no exercise of the imagination is required to bring them clearly before us. In photograph No. 8 they are all visible. The Apennines, the greatest of them, start from the eastern end of the _Mare Serenitatis_, and run in a slightly curved line southeastward, a distance of about 450 miles. They form the singular ornament which the Moon Maiden (or shall we now call her Helen of Troy?) wears upon her forehead. Turn the photograph upside down so that the moon is presented as the naked eye sees it in the sky, and you will find that, although he aimed only to be scientifically exact and to exclude everything but the real facts, Mr. Wallace has produced an excellent picture of this wonderful face in the moon.”

“But what is that face?”

“It is humanity projected upon the moon. It is a lesson on the powers of the imagination. We perceive a certain collocation of mountains, peaks, and plains on the disk of the moon, and our fancy sees in them a human likeness. We should congratulate ourselves that we are able to do this. It is a kind of proof of superiority. Many brute animals do not recognize even their own likenesses in a mirror, much less in a picture. But the Moon Maiden is perhaps as real as your inhabitants.”

“I am not prepared to confess that yet.”

“Very well, let us go on. The lunar Caucasus is the broader, but shorter, range of mountains at the northeastern corner of the _Mare Serenitatis_, and the Alps extend eastward from the Caucasus to a conspicuous dark oval close to the terminator, which is one of the most remarkable formations on the moon, and which, when we come to study it in one of the larger photographs, will probably interest you deeply because it is one of the places where recent studies have discovered indications of what may possibly be some form of lunar life. I wish now to direct your attention to the central and upper parts of the photograph. Running downward from the south, a little west of the terminator, you will perceive a double row of immense rings and ring plains. They are not only remarkable individually, but quite as remarkable for their juxtaposition in two long ranges. Among them, in the westernmost row, are three or four whose names you may remember—Maurolycus, Stöfler, Aliacensis and Werner. Still larger ones are included in the eastern row, the largest of all being at the bottom. It is rather a hexagon than a circle. It is 115 miles in diameter, and the flat plain inside the bordering mountains contains about 9,000 square miles. By close inspection you will perceive a small crater mountain near the northwestern side. This immense walled plain is named Ptolemæus after a great astronomer of antiquity, the author of the Ptolemæic system, which treated the earth as the center of the universe.

“Still more interesting are the things visible farther south. You cannot fail to remark a very beautiful ring, a perfect circle, brightly illuminated on the eastern side, and having a bright point symmetrically placed in the exact center. It is named Tycho, after another great astronomer, and is generally regarded as the most perfect crater ring on the moon. It is 54 miles in diameter, and its walls are about 17,000 feet high on the inner side, more than a thousand feet higher than Mt. Blanc, the giant of the terrestrial Alps. Its central mountain is 5,000 feet high. The most remarkable thing about Tycho is the vast system of ‘rays’ or bands which seem to shoot out from it in all directions, traversing the surface of the moon, north, south, east, and west for hundreds of miles, and never turning aside on account of any obstacle. They lie straight across mountains, valleys, and plains. We have already seen one of them, the largest of all perhaps, crossing the _Mare Serenitatis_ and the _Lacus Somniorum_, in the northern hemisphere of the moon. Nobody knows exactly what these rays mean or what they consist of. We shall from this time on see them in all the photographs that we examine, and later I shall have more to say about them, and the speculations to which they have given rise.

“About half way between Tycho and the south pole of the moon, you will see an enormous irregular plain, with lofty broken walls, interrupted by a number of crater rings. Several similar rings also appear in the interior of the plain. If Tycho is the most perfect in form of the lunar crater rings, this great inclosure, which is named Clavius, is the finest example of the walled valleys. It is more than 140 miles across, and covers an area of not less than 16,000 square miles. Two of the rings within it, which seem so small in comparison, are 25 miles across. A smaller walled plain, yet one of really immense size, is seen half way between Tycho and Clavius, and farther from the terminator than either of them. This is Maginus, and it possesses the peculiarity that at full moon it practically disappears!”

“But how can that be possible? I see nothing behind which it can be hidden.”

“It is the sunlight that hides it. You must have noticed already that the rings and mountains are best seen when at no great distance from the terminator, because there the sunlight strikes across them at a low angle, and their shadows are thrown sharply upon the adjoining slopes and levels. Look at the western part of the moon in the photograph before us. Many of the huge rings and walled plains that were so striking in appearance when the sun was rising upon them are now barely visible. Langrenus and Petavius, for instance, have become no more than whitish blotches, and even Theophilus is no longer conspicuous. The reason is because when the sunlight falls vertically upon any part of the moon there are no shadows there, and without shadows there can be no appearance of relief. Then the mightiest mountains are almost lost from sight in the universal glare. The same thing would be apparent if you were suspended above the earth at a great height in a balloon and looking down upon the tops of the snowclad Rockies. Without shadows serving to reveal their true character and to throw their outlines in silhouette upon the adjacent plains, they would resemble only white spots and lines on the generally darker expanse of the continent. But Maginus is an extreme case. Owing to the relatively small elevation of its walls, and their broken-up state, and owing also, probably, to a similarity of color between the mountain ring and the inclosed plain, when the light is vertical upon them, as at the time of Full Moon, they blend together and become barely distinguishable from one another, and from the surrounding surface of the moon.

“Take now photograph No. 9. The age of the moon here is actually less than it was in the photograph that we last examined, yet, in consequence of libration, which has caused the moon, in effect, to roll a little to one side, the sunlight is farther advanced toward the east, and we see many features of the lunar world that before had not yet emerged from night. Clavius you will notice is much more fully illuminated. See how distinctly the shadow of its vast western wall is cast upon the floor of the valley within, while the opposite eastern wall with its immense cliffs and precipices glows in full sunshine, its shadow, thrown toward the east, blending with the darkness of night still covering that side of the moon. Southeast of Tycho, which is beautifully shown here, two other great walled plains have come into view. The uppermost of these is Longomontanus and the other Wilhelm I. For a considerable distance below these (toward the north) the surface continues broken with rings and craters, but at length these give place to a dark, level expanse. This is a part of the _Mare Nubium_, or ‘Sea of Clouds.’”

“Not quite so romantic a name as some of the others,” remarked my friend, “but still I think I can be sure that Riccioli had nothing to do with the selection. There is certainly something poetic in the idea of a sea of clouds.”

“It is a very beautiful region when examined with a telescope,” I continued, “and its mountainous shores contain many interesting formations. Farther north, you will observe, near the terminator, and apparently lying in the midst of the _Mare Nubium_, a large ring, as perfect in form as Tycho itself. This is a very famous object, and it bears the name of the great astronomer Copernicus, who overthrew the Ptolemæic system and established in its place the true idea of the solar system, namely, that the sun is its center, while the earth and the other planets revolve as satellites around him.”

“Surely,” said my friend, “Copernicus deserved to have his name placed in the moon, and very conspicuously, too.”

“It could not have been made more conspicuous,” I replied, “for the situation of the great ring mountain called Copernicus, in the midst of an immense level expanse, makes it one of the most marked features of the lunar world. Copernicus is the subject of one of the larger photographs that we are going to examine later, and I reserve a description of its peculiarities. North of Copernicus you will observe apparently a continuation of the _Mare Nubium_. But it is really another ‘sea’ that we are looking upon there, the _Mare Imbrium_, ‘Sea of Rains.’ The baylike projection that runs out into the bright highlands west of Copernicus bears the name of the _Sinus Medii_, ‘Central Gulf,’ and the one just below it is the _Sinus Æstuum_, ‘Gulf of Heats,’ which is certainly suggestive of dog days on the moon. Observe that the _Sinus Æstuum_ merges on the west with a dark, oval area, which is called the _Mare Vaporum_, ‘Sea of Mists.’ It is one of the darkest districts on the moon. If you will now turn the photograph upside down you will find that the _Sinus Medii_ constitutes the dark eye of the Moon Maiden, while the _Sinus Æstuum_ and the _Mare Vaporum_ form that portion of her hair which droops upon her forehead.”

“Why not frankly call it frizzed?”

“Because I feared that you would not consider that a sufficiently poetic term.”

“But I find poetry enough in the names ‘Gulf of Heats’ and ‘Sea of Mists.’ My admiration for the man who could think of such appellations continually increases.”

“Then please reverse the photograph, for we must not lose ourselves in dreams. You will notice that the range of the lunar Apennines runs between the _Mare Vaporum_ and the _Sinus Æstuum_ on one side, and the _Mare Imbrium_ on the other. The entire chain of the Apennines is beautifully shown here. They are exceedingly steep on the side facing the _Mare Imbrium_, and gigantic peaks standing upon their long wall cast immense shadows over the ‘sea.’ Their southwestern slopes are comparatively gentle, rising gradually from the level of the _Mare Vaporum_. At their upper or southern end, in the direction of Copernicus, they suddenly terminate with a beautiful ring, which is called Eratosthenes. This is a fine example of the disk or cup shape of the lunar volcano. The bottom of Eratosthenes lies 8,000 feet below the level of the surrounding _Mare_, while peaks on its wall are as much as 15,000 or 16,000 feet in height. Between the lower end of the Apennines and the upper end of the Caucasus Mountains a strait opens a broad, level way between the _Mare Imbrium_ and the _Mare Serenitatis_. On one of the large photographs these two ‘seas’ and the strait connecting them are represented in all their picturesque details, as you will see when we come to study them. I promise you at that time a free rein to your imagination and plenty of room for its flights. On the northern border of the _Mare Imbrium_ and close to the terminator we see once more the remarkable oval valley to which I referred when pointing out the lunar Alps, and which bears the name of Plato. I call your attention to it and also, again, to Copernicus, in order that you may compare their appearance here with that which they present in the next photograph, taken when the moon’s age was eleven and three-quarter days.”

We hereupon turned to photograph No. 10.

“Now,” I continued, “observe the difference that some two days’ advance of the sunlight has produced. Plato is far within the illuminated part of the disk, and it looks darker than before. Copernicus, on the other hand, which appeared as a sharp ring with one border dark when it was near the sunrise line, has now become a round, white spot, somewhat darker in the center, with a great grayish splatter surrounding it upon the surface of the _Mare_. In the meantime, over nearly the whole extent of the _Mare Imbrium_ the sun has risen and two other _mares_ have made their appearance, one of which, extending across half the width of the eastern hemisphere, might be called the Pacific Ocean of the moon, if it had any water. It is named the _Oceanus Procellarum_, the ‘Ocean of Tempests,’ while at its southern extremity a very dark nearly circular expanse, inclosed with mountains, bears the name of the _Mare Humorum_, ‘Sea of Humors.’”

“Evidently the astronomer who bestowed that name was not in a joking mood else he would surely have called it the ‘Sea of Humor.’”

“No, apparently he was in deep earnest. But what kind of humors he was thinking of I cannot tell. Perhaps the name occurred to him because the _Mare Humorum_ is the darkest of all the great levels on the moon. It is very conspicuous to the naked eye at Full Moon. You will perceive that Tycho has now become the most prominent of all the rings on the moon. It will maintain this distinction and continue to gain in conspicuousness up to the time of Full Moon. Seen as we now see it, Tycho manifestly merits the appellation sometimes bestowed upon it of the ‘metropolitan crater of the moon.’ Notice how bright the mysterious bands radiating from it have become. The higher the sun rises upon them the more brilliantly they glow, almost as if they were streaks of new-fallen snow. They spread over the whole of the southwestern quarter of the moon, hiding rings and mountains with their brightness. One very notable ray runs down into the _Mare Nubium_, and a fainter one parallel with it produces the semblance of a long, walled way.

“The South Pole of the moon lies in the midst of a marvelously upheaved and tumbled region, where one huge ring is seen breaking into another on every hand. One of these rings, named Newton—it lies just on the upper edge of the disk, south of Clavius—surrounds the deepest known depression on the moon. Its bottom sinks to a depth of 24,000 feet below the highest point on the wall. This gigantic hole is so profound that, situated where it is, close to the pole, where the sun can never rise very high, its depths remain forever buried in night. It is the very ideal of a dungeon, for if you were imprisoned at the bottom you would never see either the sun or the earth.”

“You make me shudder! Truly, after all, the moon appears to be a world filled with dreadful things. Who would ever imagine it, seeing how serene and beautiful she is in a calm night?”

“Yet is there not a kind of beauty even in those things, like the abyss of Newton, which appall you only when you know the real facts about them? There is a certain grace in their shapes and outlines, and a great attraction for the eye in their contrasts of light and shadow. It is the same sort of attraction which we find in such terrestrial scenes as the Yosemite Valley viewed from Inspiration Point, or the awful depths and chasms of the Grand Cañon of the Colorado. The presence of man and his works is not always essential in order to fix our attention upon the wonders of nature. Their very grandeur exalts us until we forget our little race and its ephemeral achievements.”

“Still, I hope that you will show me something on the moon less awe-inspiring and suited to awaken more quiet thoughts, and especially to reassure me concerning my lunarians, as I suppose you would call them.”