FIRST QUARTER TO FULL MOON

The Moon: A Popular Treatise by Garrett Putman Serviss is part of the HackerNoon Books Series. You can jump to any chapter in this book here. FIRST QUARTER TO FULL MOON

FIRST QUARTER TO FULL MOON

NOTWITHSTANDING the signs of impatience which my friend had manifested when we were passing, in our review of the photographs, from one lunar ring mountain to another, all more or less similar in appearance and characteristics, I was gratified to see that her mind was still attracted to the subject of the moon, and during the lunch she, of her own accord, began to talk of it.

“You have said so much about volcanic occurrences on the moon,” she remarked, “that I wonder why you do not call those immense mountains ‘volcanoes.’ I observe that you always speak of them as ‘rings,’ or ‘mountain rings,’ or ‘ring plains’; while to me, although to be sure I am no geologist and have perhaps no right to an opinion, they seem plainly to be just huge volcanoes and nothing else.”

“Your observation is quite correct,” I replied, “as far as superficial appearance goes, and I may add that these great rings are often called volcanoes. If we apply the proper adjective and name them ‘lunar volcanoes,’ perhaps there can be no objection to the term. But they are certainly widely different from our terrestrial volcanoes. The difference is not in size alone, although in that regard it is enormous. There is a far more significant difference, which you could hardly be expected to notice in a simple inspection of the photographs, although it is evident when once pointed out. I refer to the fact that what seem to be the craters of lunar volcanoes are not situated on the tops of mountains. They are immense plains, more or less irregular in surface, and often having a peak or a group of peaks in the center, while around these plains always extends a mountain ring, steep on the inner side, and having a gradual slope without. But most significant fact of all, the plains, or floors inside the ring, are almost invariably situated thousands of feet below the general level of the moon. If the terrestrial volcanoes were formed on the plan of the lunar ones, when we visit Vesuvius, instead of climbing up a mountain rising out of the midst of a plain and capped with a cone, having a funnel-shaped crater in the center, we should find before us a relatively low, circular elevation, on surmounting which there would appear on the inside of the circle a great basinlike hollow, far below the level of the surrounding country. In the center of this, distant 85from the lofty encircling walls, would be seen a conical hill with smoke and vapor issuing from a vent at its summit. The top of this crater hill would be lower than the rim of the basin-shaped hollow, so that the whole volcano with its immediate surroundings would be in closed and shut off from the environing upper world by the sides of the basin. While you finish your coffee I will make a sketch which may render this difference between lunar and terrestrial volcanoes evident at a glance.”

Lunar Volcano, in Section.

Terrestrial Volcano, in Section.

Accordingly, after a few minutes, I presented to her these two diagrams, remarking that it should be borne in mind that the two sketches were not made on the same relative scale. “I was compelled,” I said, “to change the true proportions in the section of the lunar volcano, for if I had drawn them as they are in fact, the width 86of the basin would have been enormous in proportion to its depth. You will recall that I told you that such rings as Albategnius and Maurolycus are a hundred miles and even more in diameter, while their depth does not exceed two or three miles. It results from this necessary falsification of proportions in the sketch that the terrestrial volcano, although so widely different in form, appears comparable in magnitude with the lunar one. But the fact is that you could take a dozen of the largest volcanic mountains on the earth and throw them into one of the great lunar rings without filling it.”

“I am the more astonished by what you say,” remarked my friend, “because you have already told me that the moon is so much smaller than the earth. How does it happen, then, that her volcanoes are so much larger? I should think that in a little world all things would be small in proportion.”

“It is quite natural to think so,” I replied, “until you reflect upon the consequences of the smaller force of gravitation on a small world. I told you last evening that gravitation on the moon, is only one sixth as powerful as it is on the earth, and you will recall that one consequence which I pointed out was that you would weigh only twenty pounds if you were on the moon. Since the same reasoning applies to all objects in the 87lunar world, it is clear that a similar force exerted there would be able to produce enormously greater effects, as for instance in the formation of vast hollows or depressions, by violent explosions, the products of which would be thrown to immense distances. Some selenographers, which is a term applied to those who study the features of the lunar world, have suggested that in this cause alone is to be found the explanation of the giant lunar ring mountains. At some remote period of the past, according to them, the volcanic forces of the moon reached a maximum of activity and energy. The lava, cinders, ashes, and other products of ejection, were hurled to a height of scores of miles, and when this fell back at a great distance from the centers of eruption these were piled up in huge rings, fifty, eighty, or a hundred miles in diameter, while the surface of the moon within the rings sank in consequence of the withdrawal of the material thus ejected. To account for the existence of the central mountains so often found in the middle of the rings, it has been suggested that at a much later period, when the volcanic energy had become comparatively insignificant, as a result of the cooling of the interior of the moon, less violent explosions, not greater than many that have occurred on the earth, took place, and by these the central peaks were formed.”

88“You are going to think me too romantic, or too imaginative, again,” said my friend, with a smile, “but I cannot prevent myself from wondering what the inhabitants of the moon did and thought while all those marvelous things were happening.”

“I have not said that there were inhabitants of the moon.”

“No, but you have confessed that there might have been inhabitants, some time, and I should like to know whether they were there when those terrible volcanoes were formed.”

“If they were,” I replied, “they could not have survived such a universal upheaval as the surface of the moon has undergone. You have seen in the photographs that the great rings and smaller craters are scattered thickly over the moon. It is true that comparatively few are found in the level expanses called ‘seas,’ but if those regions were covered with water they could only have been inhabited by beings provided with gills and fins.”

“How long ago did these explosions occur?”

“I cannot tell you, except that it must have been many ages in the past; so long ago, indeed, that the whole course of human history seems but a day in comparison.”

“Then,” said my friend with animation, “there has been time enough since that dreadful 89period for inhabitants to develop upon the moon, has there not?”

“Yes, time enough, perhaps, provided that sufficient water and air and other vital requisites remained after the exhaustion of the volcanic energies.”

“Oh, let us say that they did remain. I am eager to believe that the moon has not always been so desolate as she appears at present.”

“Very well, you are at liberty to believe that if you like. No astronomer is likely positively to contradict you, although he may smile a little incredulously. Besides, as I have already told you, there are certain rather inconclusive indications of some kind of life, and of some kind of activity, still on the moon.”

“Please show them to me, then, or tell me about them. Perhaps I shall find them less inconclusive than you do.”

“Everything in its turn,” I replied. “We shall come to the indications that I have spoken of after we resume the inspection of the photographs.”

“Then I am ready to resume at once.”

Accordingly we returned to the table and the photographs under the pleasant shade of the elm. Taking up the photograph numbered 7, I remarked that it exhibited the moon as it appears a little after First Quarter; that is to say, a trifle 90more than half the face turned toward the earth is in the sunlight. I called attention once more to the six “seas,” which we had already remarked, and to the continued conspicuousness of Theophilus and its companions, a little above the middle of the visible hemisphere.

“You observe now,” I continued, “how the rotundity of the lunar globe begins to manifest itself as the sunlight sweeps farther eastward. The crescent shape is gone and the line between day and night begins to be bowed outward, convexly. The Mare Crisium is particularly well defined, and also the diamond-shaped region called the Palus Somnii. With the sun so nearly vertical above it, the remarkable peak of Proclus, between the Palus Somnii and the Mare Crisium, has become very brilliant. In a telescope you would see it glowing almost like a star. You observe also that several long, straight, bright rays proceed from it in several directions.”

“All the more reason, it seems to me,” said my friend, “why your unimaginative astronomer, Riccioli, should have named it for some brilliant gem instead of attaching to so dazzling an object the prosaic designation of ‘Proclus.’”

“After all,” I replied, “what’s in a name?” Now that you are familiar with the appearance of Proclus, its name will henceforth call up to your mind an image as brilliant as if it 91had been named ‘Mount Diamond’ or ‘Mount Amethyst.’”

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 92southern 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 93from 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 94must 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?”

No. 8. August 31, 1903; Moon’s Age 9.22 Days.

“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 95the 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 96its 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. 97Wallace 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 98rings 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 99remarkable 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 100the 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 101upon 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 102and 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.”

No. 9. August 2, 1903; Moon’s Age 8.97 Days.

“It could not have been made more conspicuous,” I replied, “for the situation of the great 103ring 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 104for 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. 105I 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.”

No. 10. November 30, 1903; Moon’s Age 11.78 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, 106the ‘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.

107“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. 108The 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.”

“You shall not be kept long in expectation. Turn your eyes once more to the Mare Imbrium. You will observe that its northern shore consists of a series of curves, each terminating with a promontory projecting into the sea. When looking at it I am often reminded of an entrancing view which I once enjoyed from the summit of Mt. Etna over the island of Sicily. From that great elevation nearly the whole eastern and southeastern coast of the island was visible as upon a map. The indented shore stretched away in long, graceful curves, where the blue Mediterranean contrasted sharply with the yellow sands, and the eye, wandering from Catania to Syracuse, was enchanted with the beauty of those geometric lines. But the winding coast of the Mare Imbrium is far longer than the shores of Sicily, and the mountains and cliffs bordering it are more wonderful than any corresponding scenes on the 109earth. I wish, particularly, to have you look at the easternmost of the indentations on the northern side of the mare. It bears a designation that must surely please your imagination. It is the Sinus Iridum, ‘Gulf or Bay of Rainbows.’”

“I recognize the work of my old friend the unknown astronomer. Verily he had a poetic soul! And he has written his poem on the chart of the moon, for those to read who can.”

“It is a charming landscape that the telescope reveals there,” I said, “even though no rainbows are visible.”

“But you will not deny that they may once have spanned that bay and its shores with their exquisite arches?”

“No, I shall not deny so pleasing a possibility. I will only say that it lies beyond the ken, and even outside the field, of science.”

“Then I regard it as fortunate that he was not too exclusive in his devotion to science, for then he could never have seen the rainbows with the eye of fancy, and your charts would not have been adorned with so delightful a name.”

“Let me tell you about this bay or gulf,” I said, tapping the photograph to recall her from her reverie. “You observe that it terminates at each end with a promontory. That at the western end is named Laplace, and the other Heraclides. The latter is the more picturesque. If ever you 110have an opportunity to see the moon with a good telescope do not fail to look at the promontory of Heraclides, for if you are fortunate in the choice of the time of observation when the setting sun is throwing its shadow over the adjoining ‘bay,’ you will find that the serrated outlines of the promontory represent, in a very striking manner, the profile of a woman, more sharply defined than the face of our familiar Moon Maiden, but a mere miniature in relative size. The shores of the Sinus Iridum are bordered with high cliffs, behind which rise the peaks of a mighty mountain mass. Just back of the center of the great bowed shore of the ‘bay’ appears, in the photograph, a small, bright crater ring. This bears the name of Bianchini. It is a lunar volcano, 18 miles in diameter, rising out of the midst of many ranges of nearly parallel hills and mountains, the general direction of which corresponds with that of the shore of the ‘bay.’ If there is any place on the moon where one is tempted to think that the scenes of a living world might once have been witnessed it is the Sinus Iridum and its neighborhood. Its latitude is between 40° and 50° north, corresponding with the most thickly populated zone of our own globe. The surface of the ‘bay’—once its bottom, if we admit that it was ever filled with water—is gently undulating, with winding ridges that suggest the action of tides 111and currents in sweeping to and fro deposits of sand and gravel, and piling them in long rows of bars and shallows. One can hardly help picturing in the mind’s eye waves breaking on the curving beach and dashing against the projecting rocks of the promontories; a white city seated just at the center of the shore of the ‘bay,’ near Bianchini, like Naples at the feet of Vesuvius; a rich vegetation covering the slopes of the mountain valleys, and romantic sails dotting the ‘bay’ and the neighboring ‘sea.’”

“I am very glad to observe,” interrupted my friend, “that you are not hopelessly prejudiced against my opinion that the moon has not always been ‘dead,’ as you call it.”

“I am so far from it,” I replied, “that I am half disposed to admit that she is not altogether dead even yet. But it is my duty to keep you as close as possible to the known facts. We shall see the Mare Imbrium and the neighborhood of the ‘Bay of Rainbows’ again. Meanwhile, suppose we turn to the next photograph of the series, No. 11. The age of the moon here is about thirteen days. She is fast approaching the phase of Full Moon. The first thing to which I would direct your attention now is the exceedingly brilliant point of light which has come into view near the terminator, a little north of east where the Mare Imbrium merges into the Oceanus Procellarum. 112In several ways this is the most noteworthy object on the moon. It led the famous English astronomer, Sir William Herschel, to believe that he had seen an active volcano on our satellite. He naïvely wrote in his notebook on a certain occasion: ‘The volcano glows more brightly to-night!’ Yet it is no more active than the other craters and crater rings in the lunar world. It is only extraordinarily, almost incredibly brilliant—by far the most dazzling point on the moon. It is a ring mountain, and is named Aristarchus. It has a near neighbor, barely visible in this photograph, close by toward the east named Herodotus. Herodotus is by no means remarkable for brilliancy. The central peak and a part of the floor and the east wall of Aristarchus consist of some material—nobody can tell what it is—which gleams in the sunlight, I had almost said like diamonds, although that would be an exaggeration. There are three or four other crater rings on the moon, including Proclus, which are also very brilliant, but not one of them can be regarded as a rival of Aristarchus. Its power of reflection is so great that it is even visible with a telescope in the lunar night, when the only light of any consequence that reaches it is that sent from the earth. It was, indeed, this fact which misled Herschel. He saw Aristarchus shining on the night side of the moon, and naturally thought 113that only the fires of an active volcano could have rendered it thus visible.”

No. 11. December 1, 1903; Moon’s Age 12.98 Days.

“And are you sure that he was mistaken?”

“Positively. There is no fire in Aristarchus, and has been none for ages.”

“But why do not astronomers undertake to find out what it is that makes Aristarchus so brilliant, then?”

“They have almost no data to go upon. You should be informed that even the greatest telescopes, with their highest powers, are unable to bring the moon within less than an apparent distance of say forty miles. At such a distance it is manifestly impossible to tell of what a lunar formation consists. We cannot analyze the moon with the spectroscope as we can the sun and the stars, because she does not shine with her own inherent light. We can only infer that a large part of the substance of Aristarchus consists of something which reflects a very great proportion of the light that falls upon it. If a mountain on the earth were composed of a vast mass of crystals, or of bare polished metal, we might expect it to present, when seen from the moon, some such appearance as we notice when we look at Aristarchus.

“In this photograph the Sinus Iridum, having the sun higher above it, is more brilliantly illuminated than in No. 10. Particularly you will 114notice the brightness of the line of cliffs along its eastern curve, terminating at the promontory of Heraclides.”

“That is the promontory which presents the profile of a woman’s face, if I recall correctly what you told me.”

“Yes. Please observe also that the oval of Plato is as dark as ever, while Copernicus has, if possible, increased in brightness, and the great splatter of broken rays around it seems to have extended farther over the surrounding maria. Almost directly east of Copernicus, in the Oceanus Procellarum, appears a much smaller crater ring, Kepler, which resembles a miniature of Copernicus because it, too, is encircled with a kind of corona of short, bright rays. Copernicus, Kepler, and Aristarchus mark the corners of a large triangle. Speaking of rays recalls us to Tycho. You will see that, as I told you, this wonderful formation grows in relative prominence when the period of Full Moon approaches. Its ringed wall and central mountain are obscured by their own brilliance, while the gigantic system of bright bands, or rays, which have their center of origin at Tycho, is gradually becoming the master feature of the bright part of the moon.

“I have told you that the Mare Humorum, which is very sharply defined in the picture before us, is the darkest of all the level areas that 115go under the name of ‘seas.’ It is not, however, the darkest spot on the moon. There are several places where the surface appears, at times, much duskier than in any part of the Mare Humorum. Three or four of these are clearly discernible in this photograph. They lie westward from Copernicus in the Sinus Medii, the Sinus Æstuum, and the Mare Vaporum. Their dusky hue strikes the eye at once. They give the impression of sink holes. No special name is attached to them, but they must have been evident to the first observers, with the smallest telescopes, and it is rather surprising they should have escaped special designation on the lunar charts. A fact which will especially interest you is that some observers look upon these and other dusky areas on the moon as being, possibly, indications of the existence of some kind of vegetation there.”

“But if there is vegetation there may be other kinds of life also, may there not?”

“Ah, I have not said positively that there is vegetation, but if there is then your conclusion as to other life may be correct. Glance next at the upper part of the disk along the terminator. Two or three broad oval rings have come into view there. The largest of these with its long eastern wall lying exactly on the line between day and night is an extremely interesting formation, bearing the name of Schickard. The plain 116within the ring is almost large enough to have been called a ‘sea’ or at least a ‘lake.’ It is about 134 miles in diameter, and is in reality much more nearly circular than it appears to be. Like all similar formations situated near the ‘limb’ of the moon, by which we mean the edge as viewed from the earth, it is greatly foreshortened by perspective. The scale of the photograph is, unfortunately, not large enough to reveal an unique thing in the immediate neighborhood of Schickard, toward the southeast. I refer to what, as far as its telescopic appearance goes, might be described as an enormous bubble—a bubble 54 miles in diameter. Unlike the other formations the surface of this singular ring is elevated above the general level of the moon. When we come to examine it in detail it hardly answers, perhaps, to my designation of a bubble, since the edges are a little higher than the center, giving it the form of a shallow dish. If we could visit it we should find on approaching that we were climbing the slopes of what would seem to be a chain of low mountains, and on reaching the summit we should see before us an elevated circular plain, sinking gradually toward the middle. Filled with water it would form a shallow lake lying on the top of a broad, flat mountain. There is nothing else quite like it on the moon and certainly nothing on the earth.”

117“It must have been a great curiosity in the days when the moon was inhabited, and I suppose that scientific ‘lunarians’ organized expeditions to explore it.”

“Perhaps, if you choose to regard it in that way. Now look again at the Mare Humorum. You perceive that its eastern side is lined with mountains and crater rings, while near the center of the northern border there is a conspicuous ring with a bright line running from the southern edge to the center. This is one of the most beautiful of lunar formations, and is named Gassendi. It is a favorite object for those who study the moon with telescopes on account of the great variety and singularity of the details visible within the ring. When you become a selenographer and possess your own telescope you will find few things more interesting to study than Gassendi.

“Next let us take up photograph No. 12. Here the moon is once more a little ‘older’ than before, and the sunrise line has again advanced a little eastward. This advance does not appear so rapid when the terminator is near the moon’s limb, because, on account of the rounding away of the lunar globe, the illuminated surface is foreshortened from our point of view on the earth. In this photograph you perceive that the wonderful shining mountain Aristarchus has become even brighter than it was before, or at least it is 118more conspicuous on account of the appearance of what seems to be a short ray shooting out from it in a southeasterly direction. There is also a light spot just below it which is caused by a little mountain group called the Harbinger Mountains. The bright ray connects Aristarchus with its neighbor Herodotus, of which I spoke a little while ago. There is a very remarkable feature of the moon here, not shown in the photograph, but to which I must briefly refer. It is an enormous cleft, or crack, or, if you please, cañon, which starts from Herodotus, whose northern wall seems to have been broken through to give passage to it, and goes winding across the surface of the Oceanus Procellarum with several sharp turns and angles for a total distance of nearly a hundred miles. What produced this remarkable chasm on the moon it is difficult to say. Some have suggested that it may once have been the bed of a river, but there are many serious objections to that view. Nevertheless, there seems to be little doubt that if we were to visit the moon we should find, in many ways, a striking resemblance between this prodigious cañon and that of the Colorado River.”

“And are not all these things so ancient, as far as you can tell, that, like the terrible volcanic rings, they might have been formed before the appearance of inhabitants upon the moon?”

No. 12. September 4, 1903; Moon’s Age 13.27 Days.

119“They certainly seem to be very ancient, and I cannot deny the possibility of what you say.”

“Very well, then, I, for my part, am convinced that curious eyes, filled with the light of intelligence, have peered down from the verge of that chasm into its fearful depths. If you will not permit me this flight of imagination I shall refuse to take any further interest in the moon.”

“Oh, I should not think of refusing. Imagine what you will, and draw your own inferences, only remembering that they are not supported by ascertained facts, and probably never will be. Yet for all that they may have an element of truth.”

“Pardon me for saying that your astronomical science, as far as it concerns the moon at least, does not seem to me quite satisfying. You are not bold enough in drawing conclusions.”

“On the contrary many astronomers think that some of their brethren are altogether too bold in that respect. However, it must be freely confessed that astronomical science, except perhaps in its mathematics, is not satisfying even to those who have created it. Nobody would rejoice more sincerely than the astronomer at the discovery of evidence of the former, or even the present, habitability of the moon. It is surely a great disappointment that we have not been able to settle so apparently simple a question in regard to our nearest neighbor in the sky.”

120“Then if I were a multimillionaire I should certainly devote several of my millions to the construction of a telescope great and powerful enough to reveal so interesting a secret.”

“With your great telescope you could probably render possible many discoveries at present beyond our reach. But the mightiest telescope that you could make would enable no one to see inhabitants on the moon, even if they existed.”

“Not if it magnified the moon a million times?”

“No, for optical imperfections and the disturbances to clear vision produced by our atmosphere would absolutely prohibit the use of any such magnification. And even supposing that one could use a magnifying power of 1,000,000 diameters in viewing the moon, how near do you think that would place us to the lunar surface? It would still appear to be more than a quarter of a mile away.”

“That is not much. I am sure I can see people at that distance.”

“Oh, yes, but the distinctness of view would be nothing like so great as if you were looking at the same objects on the earth. Still, if we could obviate the atmospheric and other difficulties, a magnifying power of one million would certainly enable us to discover the works of the moon’s inhabitants—their houses, their fields, 121their plantations, their great establishments of art and industry. But I assure you that a telescope of such power is a mere dream. It could never be constructed without some fundamentally new and unheard-of discovery in optics. We shall do better to turn once more to our photographs which, at least, have no deceptions. Dropping No. 12, we shall take up No. 13, which brings us practically to the Full Moon phase. The moon’s age at the time this photograph was made was nearly fourteen and one-half days. You see that its whole eastward face is now lying in the sunlight. The march of day across its surface has been completed, and on the western edge of the moon the sun is about to set, while on the eastern edge it is just rising. Among the new things that have come into view is a conspicuous dark oval, shaped like Plato, but very much larger, near the eastern edge. This is a walled plain named Grimaldi, and it enjoys the distinction of being the darkest on the moon. Near it on the northeast and consequently closer to the limb is another walled plain, which I promised some time ago to point out to you because it bears the name of the astronomer Riccioli, the great bestower of names on the moon, and upon whose lack of imagination you have so severely commented. But, as you have already learned, the time of Full Moon is not 122the best for studying the mountains and rings, because then the light strikes too nearly vertical upon them and they cast no shadows. But it is the best time for seeing the broad general features of the lunar surface. Turn the picture upside down again, thus bringing the disk into its natural position as seen with the naked eye, and this photograph shows the moon very much as it appears with a small pocket telescope, or with a powerful binocular. The new prism binoculars that have come into use within the past few years are excellent for general views of the moon. Their defining powers are superb, and one who has never seen the moon with such a glass is always greatly surprised and delighted with the view which it affords. You see now that Tycho forms a blazing brooch, resting on the Maiden’s neck, while its rays extend across her profile, and the long one lying over the Mare Serenitatis bears some resemblance to a pin displayed in her hair, with the crater ring, Menelaus, glittering at its lower end. The other bright point, to the left of Menelaus (we will henceforth keep the picture reversed), is a ring mountain named Manilius. After the detailed study which we have given to the various ‘seas’ and formations you should be able to recognize them with the picture in this position, and I wish that you should do so because, as I have just remarked, this is the 123position of the Full Moon as it is always seen with the naked eye or with a simple binocular, for the latter does not reverse it, as does a telescope. The western edge is now at the right hand, and the north at the top. All the mares are clearly visible. On the right the Mare Crisium, the Mare Fœcunditatis, the Mare Nectaris and the Mare Tranquillitatis; in the center, above, the Mare Serenitatis; on the left the Mare Imbrium, the Mare Vaporum, the Mare Nubium, the Mare Humorum, and the Oceanus Procellarum. The two bright spots on the right, lower than the Mare Fœcunditatis, are Petavius and a neighboring ring. Vendelinus forms a less brilliant spot at the western edge of an extension of the Mare Fœcunditatis, and Langrenus is distinctly seen on the western shore of the main body of that mare. Proclus and the remarkable diamond of the ‘Marsh of a Dream’ are very plain just under the large oval of the Mare Crisium. The mountains and cliffs encircling the Mare Imbrium on the west, north, and east you will recognize at a glance. The dark Plato is conspicuous in the lighter mountainous area north of this ‘sea,’ and the semicircle of the ‘Bay of Rainbows’ is sharply defined. Farther north is the long, dark Mare Frigoris, whose eastern end merges into the broad Oceanus Procellarum. Aristarchus appears as a very bright point in this ‘ocean,’ and far 124to the right of Aristarchus, toward the center of the disk, Copernicus, with its splatter of irregular rays, is conspicuous. Following the eastern limb round toward the south we see again the dark oval of Grimaldi, beyond which the bright mountainous region broadens as we approach the South Pole.

No. 13. September 5, 1903; Moon’s Age 14.40 Days.

“There is just one other thing on which I should like to dwell a little while we have the Full Moon before us. I have already referred to it once or twice—I mean the system of bright rays or bands radiating from Tycho. These rays, as I have told you, are among the greatest mysteries of the moon. Their appearance is so singular and, if I may so describe it, unnatural, that when the first photographs of the Full Moon were published, some persons actually thought that they were being imposed upon. They imagined that the photographer had indulged in a practical joke, by photographing a peeled orange and dubbing it ‘the moon.’ The mysterious rays do not start from the central mountain of Tycho, nor even from the ring itself, but from a considerable distance outside the ring. Nevertheless, Tycho is manifestly the center from which they arise. It looks as though some irresistible force had been focused at that point—a force that split the moon along a hundred radiating lines. This is, in substance, the theory of the English selenographer 125Nasmyth. He supposed that, the lunar globe being burst by internal stress, molten lava welled up and filled the cracks. After solidifying this lava possessed a lighter color and greater reflecting power than its surroundings and thus gave rise to the appearance of long bands.”

“Really, your moon history seems to me to be made up of extremely tragical chapters. But I am content as long as you put all these terrific events sufficiently far in the past to leave time for the moon to have enjoyed a different kind of history since they occurred.”

“But,” I said, “even if I grant what you wish, you must admit that the greatest tragedy of all succeeded.”

“What do you mean?”

“I mean simply that your imagined lunar age of gold, when the moon was full of animated existences and beautiful scenes, has also become a thing of the past; and what geological cataclysm can be compared in tragic intensity with the disappearance of a world of life?”

“But that disappearance was gradual, was it not?”

“Very likely it was, if it depended upon the slow withdrawal of the atmosphere and water.”

“Good! Then again I am fairly well content, for all things must have an end. The most beautiful life finally merges into old age and death. 126I think I have read that some of your savants predict that the earth will not always be a living world. All that I ask is that you leave room somewhere in your lunar history for an age of life on the moon.”

“Very well then. As I have told you several times, Science does not positively forbid you to picture such an age if you will. She only says that she cannot find the evidences of its existence. Still, as we are going to see later, there are those who think that they can perceive indications of some simple forms of life on the moon even now. I will grant you that in the past these may have been more numerous and more highly organized.”

By this time the afternoon had waned and the trees were lengthening their shadows upon the lawns of the park.

“Perhaps,” I said, “we had better postpone an examination of the remaining photographs of the series exhibiting the moon’s various phases until after dinner. They will show very well in the light of the electric chandelier. I have but a few words to add concerning the rays of Tycho. The opinion of Nasmyth concerning their mode of origin has not been universally accepted. Prof. William H. Pickering, for instance, has suggested that the rays are formed by some whitish deposit from the emanations blown out of comparatively minute craters lying in rows. He 127supposes large quantities of gas and steam given forth from craters surrounding the rim of Tycho, and, in consequence of these gases and vapors being absorbed and condensed in more distant regions, a wind constantly blowing away from Tycho and distributing the white deposit in windrows. A similar explanation has been applied to the shorter and more irregular systems of rays surrounding Copernicus, and a few other ring mountains.”

“I prefer the Nasmyth hypothesis,” said my friend, as we rose and took the path to the house. “It is, to be sure, more gigantically tragic, but then it is simpler and more easily comprehended.”

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