Part 7

“Excellent!” I said, producing my portfolio. “Here then are the photographs which I trust will enable us, in imagination, to spend an interesting month upon the moon. These photographs were made at the Yerkes observatory and they represent the moon, as you will perceive, in all of her principal phases, beginning with the narrow crescent of the New Moon, and ending with the similar, but reversed, sickle of the Old Moon.”

“Let us take them out into the park under the trees,” my friend suggested.

The shafts of morning sunshine, falling through the branches and illuminating the broad lawns and brilliant flower-beds, offered the greatest possible contrast with the strange scenes of the preceding night. We chose the shadow of a huge elm, and had a table placed there for our accommodation. On this I spread the photographs, and my companion began to examine them with many expressions of interest.

“It is not often,” I said, “that science finds so flattering an audience.”

“And I hope, surely, never so small a one,” she responded, laughing. “But you must admit that science very seldom presents herself in so attractive a form as that of these pictures.”

“They are indeed of the highest excellence,” I replied. “It is the very moon herself that you see there.”

“But are you certain that they have not been embellished? Has not the hand of an artist retouched and improved them—particularly these large ones that seem to contain a thousand curious things which I can hardly believe really exist on the moon?”

“No,” I said, “there is nothing fictitious or imaginary in what you see. The only art displayed here is that of the astronomer-photographer, whose greatest ambition is to make his pictures absolutely true to nature. A defect in one of his plates, producing the appearance of a speck of light or shadow which does not actually exist, causes him as much distress of mind as you would experience upon hearing a false note from your piano. Indeed, the astronomer is so desirous of having nothing but the truth represented in his pictures that he often prefers, for his own study, the original negatives alone, because every time that they are reversed to make a ‘positive’ copy something is sure to be lost, and some slight defect is certain to be introduced. Let us begin, if you please, with the series of smaller pictures showing the various phases, and the gradual advance of daylight across the moon’s surface. Take first the photograph which I have labeled No. 1. It shows the New Moon when it is between three and four days old. You must often have seen it in that form in the western sky soon after sunset. Photographs of the New Moon have been made when the crescent is still narrower than that here shown, but there is no such photograph in this series, and it would possess little interest for you because almost no details of mountains, craters, and plains would be visible. It is hardly possible to make a good photograph of the moon when it is only one or two days from the sun in its monthly journey, on account both of the glare of the solar light in our atmosphere and of the nearness of the moon to the horizon, where the air lacks transparency and steadiness. In the photograph before us you will observe a great number of strange forms and shadings. I shall tell you what these are presently, but first let me call your attention to the fact that the picture does not exhibit a phenomenon which you would behold if you were actually looking at the moon in the phase here represented. You see here the New Moon very clearly, but not the Old Moon in her arms.”

“Indeed! It is a pity that the photograph does not show so interesting a sight.”

“Yes, it is a pity. The cause lies in the defect of light from what I have called the ‘Old Moon.’ The part that we see in the photograph is illuminated with sunshine, while the remainder of the moon reflects only the earthshine, which is too faint to be photographed (at least with the amount of exposure required to make a good picture of the brightly lighted crescent); although, as I have said, you would see it clearly if you were looking at the New Moon herself.”

NO. 1. FEBRUARY 19, 1904; MOON’S AGE 3.85 DAYS. ]

“But,” interrupted my companion, “do you mean to tell me that the earth illuminates the moon?”

“Surely it does. Why not?” I replied, smiling. “You must remember that the earth is simply a huge moon to our imagined inhabitants of the lunar world. Our globe sends to the moon about fourteen times as much reflected sunlight as the moon sends to the earth. The consequence is than an earthlit night on the moon is far more brilliant than a moonlit night on the earth.”

“Then why do we not always see the moon shining with light from the earth?”

“It is a question of contrast. You cannot see a faint light in the immediate presence of an overpoweringly brighter light. The part of the moon that the sun illuminates is in the full glare of day, and this is so much more brilliant than the reflected earthlight that that portion of the moon which enjoys only the latter is not visible to us, except for a few days after New Moon, when the amount of light from the crescent is not yet great enough to dazzle our eyes and hide the rest from sight. I should advise you when the next New Moon occurs—you can find the date in any almanac—to look at it in the western sky. You will see in addition to the bright crescent the full round orb of the moon, shining faintly, with a dull, rather copperish, tint, and you will find it interesting, then, to remember that that light is reflected from our earth.

“And now,” I continued, “let us examine our photograph more closely. There is one remark that I had expected which you have not made; it concerns the position of the crescent. You observe that it is bowed toward the left. If you saw it with the naked eye in the sky it would be bowed toward the right, or toward the place of sunset. The reason is that the photograph presents the moon as seen with a telescope, which reverses objects, turning them top for bottom. In this picture, and in all the others that we shall examine, the southern part of the moon is at the top and the northern part at the bottom, the western part at the left and the eastern part at the right. The first thing that you probably notice in the photograph is a conspicuous oval plain, somewhat below the center of the crescent.”

“Yes, and I see clearly why you call it a plain, for it is perfectly flat and smooth.”

“Not quite so flat and smooth as you suppose. This object is one of the most celebrated on the moon. It is the so-called Mare Crisium, or Sea of Crises, as we may translate the name given to it by the astronomers of a couple of centuries ago, many of whom knew more Latin than science. Owing to its apparent smoothness of surface, as well as to its form and general aspect, they took it for a great lake or sea.”

“To tell you the truth,” said my friend, “if I were an astronomer and had discovered this curious place on the moon, I should certainly believe just what your Latin-loving predecessors believed, but I doubt if I should have been capable of inventing so singular a name for it.”

“In the singularity of the names they chose for objects on the moon,” I replied, “their invention is unrivaled. We shall see some remarkable examples. Of course they are not at all to be blamed for thinking that this oval spot, and other similar ones of much greater magnitude, were seas and oceans. They simply judged by appearance and by analogy. Finding mountains on the moon, they saw no improbability in supposing that there were bodies of water also. They had not the means of knowing, as we know to-day, that there is no water on the moon. Yet, perhaps, they were not so far wrong after all. The Mare Crisium certainly has the look of an empty sea bed, and I should not be willing to assert that ages ago it was not filled with water.”

“Like the Great Salt Lake, dried up,” suggested my companion.

“Not exactly, for the Great Salt Lake dried up would probably present a surface as white as snow, whereas the Mare Crisium is very dark. It must be admitted, however, that gradually the white deposit would grow darker, and there may be much significance in the fact, which some observers have noticed, that, at times, parts of the dark plains on the moon seem to glitter with minute points of light. Your imagination is at liberty to see deposits of salt there.”

“In that case,” said my companion, laughing, “I should prefer to regard the Mare Crisium as resembling that wonderful valley discovered by Sindbad the Sailor, whose floor was sprinkled with diamonds.”

“Well,” I replied, “science certainly cannot deny the possibility of diamonds on the moon, for she is par excellence the world of volcanoes, and one of the most striking discoveries of recent years is that of the intimate association existing between ancient volcanic vents and deposits of diamonds. The diamonds of South Africa are found in lava rocks that cooled off ages ago.”

“Then I hope that no future Columbus will find a way to the moon, for we should have too many diamonds, and they would lose all their charm.”

“That is true, but suppose that not only diamonds but even more beautiful gems should be discovered in the lunar world? You surely would not object to a transethereal traffic bringing them to our doors. However, there is not the slightest prospect that we shall ever be able to go from the earth to the moon. Let us resume our examination of the photograph, and concentrate our attention on the known facts.”

I then proceeded to tell my friend, whose interest I was delighted to find had not yet begun to flag even in the face of comparatively matter-of-fact statements, that the Mare Crisium is a profound depression, about 350 miles in length by 280 in breadth. Exactly how far it lies below the general level of the lunar surface we do not know; but, at any rate, if it was ever filled with water it formed a deep, navigable sea. Its encircling mountains, which appear generally bright in the photograph, especially along the eastern border, where the sunlight strikes directly against their slopes, are in many places steep and abrupt. At one place, on the southwestern side, there is a mountainous promontory 11,000 feet in height. There are a number of small craters on the floor of the Mare Crisium, but the scale of this photograph is not large enough to show them clearly.

“You will notice,” I continued, “that there is a kind of bay on the eastern side, which runs back into the mountains, and is bordered with high, steep cliffs. Near this point, on that part of the moon over which the sun has not yet risen, there is a very remarkable mountain which we shall see in a later photograph. But let us finish with this one. Look at the comparatively small oval adjoining the Mare Crisium below (toward the north). It is one of the great crater rings of the moon, and is named Cleomedes. It is much larger than it looks, being nearly 80 miles in its greatest diameter, and there is a peak on its surrounding wall 10,000 feet in height. Still farther toward the north you will observe two or three other smaller craters or rings, which are very interesting when studied with the telescope.