WHAT IS IT LIKE?—MOON SUPERSTITIONS—DESCRIPTION OF THE MOON—PHASES—TIDES—ECLIPSES. From the early days of childhood every man and woman has been familiar with the moon. This satellite of earth has been domesticated, so to speak, amongst us; and while the sun and other stars have been glorified in poetic and prose effusions, the moon has been always more tenderly addressed. The soft (reflected) light of our attendant moon is much more attractive than the brilliancy of the greater light “that rules the day.” The moon is regarded as our particular property, and has awakened an interest in our minds since the time that we could, as we fancied, see the “Man in the Moon.” In ancient times the moon was supposed to possess some light of her If it were possible to reach the moon, as M. Jules Verne’s travellers did, we should find a very irregular and corrugated surface—plains and mountains without water. We should be able to see the stars in the daytime, because there is no atmosphere around the moon, and there is a silence that “might be felt.” The appearance of our earth from the moon, and the beauty of the stars in the unclouded and waterless space around the satellite, must be very grand, and has been, in a measure, depicted in the illustration (fig. 559) on the opposite page. In this illustration (fig. 560) we have some idea what the moon is like. We see the rugged and cratered appearance of the disc; it is a desert waste, so far as we can ascertain, without inhabitants, and, in all probability, without vegetation. For there being no moisture amongst the plains and craters and mountains of our satellite, we must conclude that the moon is dead. It is a very interesting,—nay, a fascinating study. When we take up our telescope and look from the window at the heavens the most beautiful object within our small telescopic vision is the moon shining like a silver plate, and we wonder what is up there. With a small telescope even we can discern many interesting features in the moon at the full, which will assist us in verifying the diagrams in books and their explanations. As the moon is only a few miles away, comparatively speaking, and as the large telescopes now in use bring us within a measurable distance of the surface, we are enabled to speak more positively about our changeable satellite than of any of the planets. When we look steadily at the full moon As is well known, water has a great erosive power, and its action disintegrates the surface of the earth with rapid persistency. So the physical appearance of the globe has become much changed in the course of ages: ravines exist where plains used to extend, and rivers cut their way through deep gorges to the sea. The sands and other deposits are overlaid, and thus the whole outward appearance has been altered. Not so the moon. With a very attenuated atmosphere without clouds or rain, there is no moisture, no lake, no water in the moon now. What may have been we can only conjecture. If there ever have been lakes or seas they have all been absorbed. The heat upon one side of the moon must be very great at one period, and the cold on the opposite side intense, as one would think—yet upon this fact authorities differ somewhat. If the moon possess no atmosphere of any kind it would be fearfully cold and extremely hot at intervals, but a surrounding medium, even of very little density, would modify the extremes; and while we must accept the fact that the temperature varies very much we need not place it above 100° of heat, nor below 20° of cold. So from close observation and comparison we are enabled to form a very fair opinion of the The moon, as all are aware, moves round the earth attendant upon us, but entirely under the control of the sun; our satellite, moreover, has been the subject of many superstitions. A great many rites and even domestic actions—such as the killing of fowls—were regulated by the moon; and in Scotland, Scandinavia, and other portions of Europe, she has always been regarded as effecting destiny. There are many interesting myths connected with the moon, and indeed with astronomy generally, and from a volume entitled “Notes on Unnatural History,” some very amusing extracts might be made. It will not be out of place to mention a few of these myths. The Chinese have an idea that a rabbit exists in the moon, and is the cause of the shadows we see. The Buddhists think a holy hare is up there. In the Pacific Islands there is a belief of a woman in the moon; she was sent there because she wished her child to have a bit of it to eat; and Mr. Buchanan has versified the old Scandinavian myth about the two children kidnapped by the moon as they returned from a well with a bucket of water slung upon a pole. The Jews placed Jacob in the moon, and the Italians say that Cain inhabits the luminary with a dog and a thorn bush. In the Inferno of Dante this is referred to, and we know that in A Midsummer Night’s Dream we have the moon coming out to shine upon the loves of “Once a warrior, very angry, Seized his grandmother, and threw her Up into the sky at midnight. Right against the moon he threw her, ‘Tis her body that you see there.” But modern scientific research has exploded all these charming old myths, and laid bare the facts for us. We must now resume. The link Moon leads to a list of the formations The moon moves around us in 27d 7h 43m 11·461s. Its diameter is about 2,160 miles, and it is much less dense than our earth, and so the force of gravity is less there than here. Its mean distance from us is 238,833 miles. The moon goes through certain changes or phases every twenty-nine days or so; and while rotating on its own axis our satellite goes round the earth, so that we only see one side of the moon, inasmuch as the two We append a map of the moon, on which the mountains, seas, and craters can be perceived, according to the list. The hill ranges extend for hundreds of miles, and the elevation reaches 30,000 feet, and even more in places. The so-called craters do not resemble volcanoes when viewed closely, but take the form of basins or valleys surrounded by lofty hills. One great plain called Copernicus is more than fifty miles across. Respecting the appearance of the moon let us quote Mr. Lockyer. “Fancy a world without water, and therefore without ice, cloud, rain, snow; without rivers or streams, and therefore without vegetation to support animal life;—a world without twilight or any gradations between the fiercest sunshine and the blackest night; a world also without sound, for as sound is carried by the air, the highest mountain on the airless moon might be riven by an earthquake inaudibly.” Phases of the Moon. We have said that the moon revolves around the earth in the same The time intervening between one “new” moon and another is 29d, 12h, 44m, 2s, and is termed a synodic revolution. This is longer than the sidereal revolution, because the earth is also moving in the same direction and the moon has to make up the time the earth has got on in front, as it were. So the moon travels nearly thirteen times round the earth while the latter is going round the sun. The revolutions of the moon have been a measurement of time for ages, and her varying appearances during lunation are always observed with interest. The illustration (fig. 567) will assist us materially. The sun’s rays fall in a parallel direction upon the earth and moon, and let us suppose that S is the sun in the diagram and T the earth; C at the various points is the moon, the capital letters, A, B, C, etc., indicating the planet as she appears from the sun, and the small letters show how she appears to us from the earth. Let us suppose that the sun, earth, and moon are in conjunction—or in The moon’s phases may be easily shown by means of a medium-sized lamp to represent the earth, a smaller one to serve as moon, and a light to act as sun all at the same height. Colour the “lunar” globe white, and if we move it about the “earth” globe, we shall see the various phases of the moon in the sharp shadows. The Tides. The ebb and flow of our tidal waters depend upon the moon to a great extent. The phenomenon is so common, that we need only refer to it, but the cause of the tides may be stated. Twice every day we have the tides twelve hours apart, and the flow and ebb are merely examples of the attraction of gravitation, which is exercised upon all bodies, either liquid or solid. The tides are highest at the equator and lowest at the poles, because the tropics are more exposed to the influence of the lunar attraction. By the small diagram (fig. 569) we shall be able to see in a moment how the moon acts. The moon being nearer to the earth at b, the water will be naturally attracted to the ball, m, and cause high water (a); and a similar effect will be produced opposite, because the earth is attracted, so the waves are higher than the ground which has been attracted away from the water, and the waters will flow in and cause a high tide at d, but not so high a tide as at the opposite point, a. It can then be understood that there will be low water at the other two sides, e and f, because the water has been taken away, so to speak, for the high tides at a and d. We shall learn more of this under Physical Geography. The moon revolves round the earth in a changeable elliptical orbit, intersecting the ecliptic at certain points called Nodes. When the moon is nearest to the Earth she is said to be in perigee Eclipses. We have briefly considered the Sun and Earth and the Moon separately. We are now about to regard the effects produced by them when they come in each other’s way and cause Eclipses, which are observed with so much interest. There are eclipses of the sun and of the moon. The former occur at the time of new moon, and the latter at full moon; and this will be at once understood when we remember that the sun is eclipsed by the moon passing between us and the sun; and the moon is eclipsed because the shadow of the earth falls upon her when she is opposite the sun, and therefore “full.” Readers of the voyages of Columbus will remember that he managed to obtain supplies from negatively hostile Jamaica savages by pretending to cause an eclipse of the moon, which he knew was about to take place, and to the ancients eclipses were of dire portent. Even in enlightened Rome, to ascribe an eclipse to the causes of nature was a crime. The Chinese have an idea that great dragons are devouring the moon when she is eclipsed. There are total, partial, and annular eclipses. The former terms speak for themselves; the latter name is derived from “annulus,” a ring; for a ring of light is left around the dark portion eclipsed, and is only seen in solar eclipses. In one sense the eclipse of the sun is really an eclipse of the earth, because it is caused by the shadow of the moon falling upon the earth. If a bright body, A, be larger than the dark body, B, there will be two kinds of shadows—viz., the umbra and the penumbra. For instance, the umbra is the central dark part in the cut (fig. 572), and the penumbra is the lighter portion. As soon as the eye is placed on the umbra, it can perceive no part of the source of light, A, which appears to be eclipsed. On the other hand, the penumbra originates in that locality where only a portion of the light proceeding from a luminous object can fall; hence an eye in the penumbra would see a part, but not the whole of the illuminating body. This shadow also forms a cone, the apex Lunar Eclipse.—Let A (fig. 573) be the sun, and B the earth, the length of the umbra of the latter will exceed 108 diameters of the earth. Since the moon is only about thirty terrestrial diameters distant from the earth, and as the diameter of the earth’s shadow, at this distance, is nearly three times as large as the apparent diameter of the moon, it follows that when the latter enters this shadow, she must be totally eclipsed, for at those places where the moon’s shadow falls there is total eclipse. If the moon’s orbit were coincident with the ecliptic, or if both moon and earth moved round the sun in the same plane, there would be an eclipse at every conjunction, and at every opposition,—i.e., a solar eclipse would happen at every new moon, and a lunar eclipse at every full moon. But we have seen that the lunar orbit cuts the ecliptic only in two points; consequently an eclipse of the moon is possible only when, at the time of opposition, the moon is in one of her nodes, or in close proximity to it, which can only occur twenty-nine times in the space of eighteen years. A lunar eclipse begins on the eastern margin of the moon, and is either total, when her whole disc enters the umbra, or partial, when only part of her disc is in the shadow. A total eclipse may last for two hours. We shall understand this better, perhaps, with the diagrams. Solar Eclipses.—When the moon and the sun are in conjunction, the moon’s place may be represented by M (fig. 574) between the earth, T, and the sun, S. If this conjunction occur when the moon is in one of her nodes, or within 16° of it, the shadow of the moon will fall upon the earth, and the sun will be eclipsed. At other places the sun will not be entirely covered; and if the moon be moved farther off, so that its shadow will not reach the earth, and so not cover the sun up completely, we shall have an annular eclipse, because a rim of the sun will be visible. The lunar umbra extends from the moon by a space about equal to her distance from the earth, and hence only a small portion, d, of the earth’s surface enters the lunar umbra. To the inhabitants of this part of the earth the sun will be totally eclipsed, and the eclipse will be annular if only the margin of the sun’s disc remain uneclipsed by the lunar shadow. This is only possible when the moon is in her apogee, or greatest distance from the earth, where her apparent diameter is less than that of the sun, which it cannot in general exceed more than 1´ 38. Hence the duration of a total eclipse of the sun cannot be more than 3¼ minutes. On the contrary, the penumbra of the moon is diffused over a much larger portion, n m, of the surface of the earth, since its section is five-ninths of the earth’s diameter. The inhabitants of this portion of the earth do not receive light from all parts of the sun, consequently a part of this luminary is invisible to them, and the eclipse is said to be partial. Solar eclipses commence on the western margin of the sun, and advance to the eastern. On account of the proximity of the moon to us, an eclipse of the sun is, in all places above the horizon of which the sun appears, visible neither at the same time, nor is it of equal duration, nor of equal extent: in some parts it may not be visible at all. In favourable situations, the diameter of the umbra, where it reaches the earth, amounts to about 167 miles, and on this small strip of the earth’s surface only can the sun appear totally eclipsed. |