THE MOON

The Moon is the Earth’s only satellite, and by far the nearest body in space to our Earth. Many astronomers are inclined to think that the Moon at one time formed a part of the Earth, but was wrenched away from it, leaving a huge cavity, which is now occupied by the Pacific Ocean. The Moon is a cold body, emitting no light or heat of its own; all the light which it seems to shed is entirely reflected light—reflecting the sun’s rays, much as a mirror might reflect them; hence its beautiful silver color.

In round numbers, the Moon is approximately 240,000 miles distant from us in space—the distance varying from 221,600 miles to 252,970 miles—causing a corresponding variation in its apparent diameter and parallax.⁠[A] The circumference of the Moon’s orbit is a little more than a million-and-a-half miles, and it travels through space with the velocity of 2,288.6 miles per hour, or 3,357 feet per second.

Our satellite always keeps the same face turned towards the Earth, so that we only see one side of it; the other side is forever hidden from the sight of man. However, the axis of the Moon tilts, in relation to the earth, and permits us to glimpse a little more of the surface both north and south, so that about five-eighths of the surface has actually been observed.

The surface of the Moon has been subjected to intensive study, and its “geography” is now as well known as that of our own earth. Vast “seas” (i. e.) sea bottoms, mountain ranges, solitary mountain peaks, enormous craters, are readily observed, and modern telescopes have now brought the moon so close to us that it has been said that any body as high as the Woolworth Building, in New York, would cast a shadow which could be observed and noted.

The fact that the same face of the Moon is always seen by man does not mean that this body remains stationary; it revolves on its own axis, from west to east, but this revolution occupies exactly one siderial month. The result is that the days and nights on the Moon, are many times the length of our days and nights. The surface exposed to the sun’s rays must get extremely hot, and, when deprived of these rays, extremely cold. It has been estimated that the mean temperature of the moon’s surface must approximate 200° F., during the “day” time, and approach the intense cold of inter-stellar space during the “night” (perhaps -250° C.). This would render life or vegetation of any kind very unlikely. However, Professor Pickering has lately asserted that vegetation does apparently spring into being with extreme rapidity during the moon’s day time—evidently remaining latent during the intense cold of the “night.” (Some interesting material on this topic may be found in Shipley’s “Is the Moon a Dead World?” No. 557 of the present series.)

The volume of the Moon is about one-fiftieth that of the earth, but its mass is only about one-eightieth that of our planet. The Moon is practically devoid of atmosphere, which is another reason why it cannot support “life,” in our sense of the word. Two theories have been advanced as to the absence of the moon’s atmosphere: (1) that it gradually combined, chemically, with the materials on its surface; and (2) that it gradually escaped into space, because of the low gravitational pull of the moon. There is no water on our satellite, which means that there is no ice and no snow. The moon being so much smaller than our earth, the pull of gravity is of course much less also.

Yet it is well known that the tides, on the earth, are greatly influenced by the moon. Every atom composing our satellite must exert some subtle pull upon every atom of our oceans, in order thus to affect them. What is the nature of this attraction? Here we encounter the mystery of gravitation! This question must accordingly be postponed until we come to our discussion of that subject.

One of the most remarkable and distinguishing characteristics of the moon consists in the so-called “lunar craters,” which appear to be immense, extinct volcanoes. More than 30,000 of these have now been mapped, varying in size from small hills to immense basins 50, 60, 100 miles in diameter. Ptolemy is 115 miles across, while Theophilus is 64 miles in diameter and 19,000 feet deep. The curious thing about these lunar craters is that they are unlike the hilly volcanoes known to us on our earth. They are rather huge circular pits, often square miles in extent, surrounded by a circular wall, and almost invariably having a single mountainous cone in the center.

Various theories have been advanced by way of explanation of these craters. The most important of these are (1) that they represent extinct volcanoes; (2) that they indicate spots where masses of matter have dashed into the moon, from surrounding space; and (3) that they represent the surface of the moon, when it was a hot, seething mass—their resemblance to the “bubbles” formed at the surface of boiling glue, mud, etc., being pointed to as analogous. Unanimity of view does not exist even yet as to their origin.

The ever-changing “phases” of the moon have been observed by generations of lovers. Thus, the new moon, full moon, etc., are commonplace sights. These apparent changes are, of course, due entirely to the relative position of the sun at the time. If the sun illumines the whole face of the moon, as viewed from our earth, we have full moon; if only a small portion of it, we see the first quarter, etc. The whole disk of the moon may always be seen, however, by careful observation. It is hardly necessary to say that the so-called “Man in the Moon” is a mind’s eye picture, created by the configuration of the various mountains, seas, etc., upon its surface.