Lunar phase

“ The teeth are shaped like equilateral triangles and square shanks are used, exactly as with the Antikythera machine. Horse-headed wedges are used for fixing; a tradition borrowed from the horse-shaped Farās used to fasten the traditional astrolabe. Of special interest for us is the lunar phase diagram, which is just the same in form and structure as the lunar volvelle that occurs later in horology and is still so commonly found today, especially as a decoration for the dial of grandfather clocks. ”

“ This small rocky world, which tells us a story full of impacts, orbits the Earth in 27.32 days. It is called the sidereal period. As the Earth revolves around the Sun, the time between two identical lunar phases is known as the synodic period, and it lasts 29.53 days.
Perhaps, you may notice the shape or shapes of the Moon that we see are always the same way. That is because the Moon always shows the same face to Earth, so we always see the same half of it. ”

“ This method also allows the calculating of the depth of craters and cavities on the moon. Galileo used it, and since Messrs. Boeer and Moedler have employed it with the greatest success.
Another method, called the tangent radii, may also be used for measuring lunar reliefs. It is applied at the moment when the mountains form luminous points on the line of separation between light and darkness which shine on the dark part of the disc. These luminous points are produced by the solar rays above those which determine the limit of the phase. ”

“ In the nineteenth century as well as in the dark ages, in London as well as in the ends of the earth, men of all colours and clans are found turning their faces heavenward to read their duty and destiny in the oracular face of the moon. Many consult their almanacks more than their Bibles, and follow the lunar phases as their sole interpretation of the will of God.
Among those who worship the moon as a personal deity, whether beneficent or malign, its influences are of course welcomed or dreaded as the manifestations of supreme power. ”

“ The intimate relation between the lunar phases and the number of examples killed was shown by statistics from 1888 to 1894. Out of 673 specimens received only 116 were killed when the moon was more than half full. ”

“ It is evidenced by the tides, by the cyclic changes in many forms of disease, which coincide with the lunar phases; it can be traced in the growth of plants, and is very marked in the phenomena of human conception and gestation. The importance of the Moon and its influence on the Earth were recognized in every ancient religion, notably the Jewish, and have been remarked [pg 203] by many observers of psychical and physical phenomena. But, so far as Science knows, the Earth's action on the Moon is confined to the physical attraction, which causes her to circle in her orbit. ”

“ That educated people to whom exact weather records are accessible should still find satisfaction in the fanciful lunar rule, is an interesting case of intellectual survival." I am willing to be with the foremost in combating such absurdities as "Herschel's Weather Table," and all theories which would assign to the lunar phases an immediate control of our weather; but it so happens that the notion Dr. Tylor condemns is one for which there may be some foundation. A moon's quarter is roughly equivalent to a week, and Mr. ”

“ Many of the mountains of the moon are, foot for foot, as lofty as the highest mountains on the earth, while all of them, in proportion to the size of the moon's globe, are much larger than the earth's mountains. It is obvious, then, that the sunshine, as it creeps over these Alpine landscapes in the moon, casting the black shadows of the peaks and craters many miles across the plains, and capping the summits of lofty mountains with light, while the lower regions far around them are yet buried in night, must clearly reveal the character of the lunar surface. ”

“ As a natural proceeding, we find that the moon has influence when the child is weaned. Caledonian mothers very carefully observe the lunar phases on this account. Jamieson tells us that "this superstition, with respect to the fatal influence of a waning moon, seems to have been general in Scotland. ”

“ And for that cause Saturn, having a wider orbit, is borne round it in a longer time, Jupiter a shorter, and Mars still less; while Venus takes nine months, Mercury 80 days, on the hypotheses of Copernicus; the Moon going round the Earth with respect to the Sun in 29 days, 12 hours, 44 minutes. We have asserted that the Earth moves circularly about its centre, completing a day by an entire revolution with respect to the Sun. The Moon revolves in a monthly course around the Earth, and, repeating a conjunction with the Sun after a former synodic conjunction, constitutes the month or Lunar day. ”

“ In other words, if a race of beings resembling ourselves, or resembling any of our contemporaries in terrestrial life, ever existed upon the moon, they must long since have perished. That such beings may have existed, is possible, particularly if it be true, as generally believed, that the moon once had a comparatively dense atmosphere and water upon its surface, which have now, in the process of cooling of the lunar globe, been withdrawn into its interior. ”

“ It might seem, that, since the moon rotates on her axis in about twenty-seven days, the lunar day ought to be twenty-seven days long, instead of twenty-nine. There is, however, a solar, as well as a sidereal, day at the moon, as on the earth; and the solar day at the moon is longer than the sidereal day, for the same reason as on the earth. During the solar day the moon must make both a synodical rotation and a synodical revolution. ”

“ It would be seen to pass through its phases, just as does our satellite, once in a lunar day or a terrestrial month, and during that cycle of phases, since 29 of our days would be occupied by it, the axial rotation would bring all the 162 features of its surface configuration into view so many times in succession. But the greatest beauty of this noble moon would be seen during the lunar night, in considering which we shall again allude to it; for when it is full-moon to the earth it is new-earth to the moon. At lunar midnight this globe of ours is fully illuminated ”

“ Hence, even at this period of the moon, her whole face becomes visible to us, but its light is not uniform or of equal intensity. The thin crescent on which the full blaze of the solar light falls, is very brilliant and distinctly seen, while the other part, on which falls only a comparatively feeble light from the earth, appears very faint, and is little more than visible to the naked eye, but with a telescope of moderate power,—if the atmosphere be very clear—it appears beautifully distinct, so that the relative positions of many of the lunar spots may be distinguished. ”

“ But in another instant the commotion was over, and the world whose curious spectacles had been enacted as if on the other side of a window, seemed to retreat swiftly into space, until at last, emerging from a fleecy cloud, it reappeared in the form of the full moon hanging in the sky, but larger than is its wont, with its dry ocean-beds, its keen-spired peaks, its ragged mountain ranges, its gaping chasms, its immense crater rings, and Tycho, the chief of them all, shooting raylike streaks across the scarred face of the abandoned lunar globe. ”

“ Now it is found that when at birth the Moon is increasing in light, that is, going towards the full, and above the horizon, or conversely, decreasing in light and below the horizon, the period from birth to inception is less than ten lunar months by a quantity determined by the Moon’s distance from the horizon. But when the Moon at birth is found to be decreasing and above the horizon, or increasing and below the horizon, the period of time from birth to inception is found to be more than ten lunar months by a quantity determined by the Moon’s distance from the horizon. ”

“ Assuming the moon to have been once in a fluid state, it is demonstrable that the attraction of the earth would accumulate a mass of matter, like a tidal elevation, in the direction of a line joining the centres of the two 32 bodies: and as a consequence, the real shape of the moon must be an ellipsoid, or somewhat egg-shaped body, the major axis of which is directed towards the earth. That some such phenomenon has obtained is evident from the coincidence of the times of orbital revolution and axial rotation of the lunar sphere. ”

“ And taking into account the whole effect of them, we may conclude that our view of the moon’s surface, instead of being confined to one half, is extended really to about four-sevenths of the whole area of the lunar globe. The remaining three-sevenths must for ever remain a terra incognita to the habitants of this earth, unless, indeed, from some catastrophe which it would be wild fancy to anticipate, a period of rotation should be given to the moon different from that which it at present possesses. ”

“ Then, too, regarding the moon as a timekeeper, we must not forget the service that it renders in furnishing a division of time intermediate between the day—which is measured by the earth’s rotation—and the year, which is defined by the earth’s orbital revolution. Notwithstanding the survival of lunar reckoning in our religious services, we, in our time and country, scarcely need a moon to mark our months ”

“ On the other hand, as has also been shown in the preceding chapter, the error of [Pg 91] the lunar cycle is one day in 300 years; so that at the end of every 300 years the full moons will fall one day earlier, for example, on the 11th of the month instead of the 12th. Now, when both equations occur together, they compensate each other; that is, while the solar equation would cause the full moon to fall on the 13th, the lunar equation would make it fall on the 11th; therefore, no correction is to be made—there is nothing to correct. ”

“ The sun, as we know, pours down its heat unintermittingly for a period of fully 300 hours upon the lunar surface, and the experimental investigations of Lord Rosse, essentially confirmed by those of the French observer, Marie Davy, show that under this powerful insolation the surface becomes heated to a degree which is estimated at about 500° of Fahrenheit’s scale, the fusing point of tin or bismuth. ”

“ We have only to recall the splendors of a night that is lighted by a full moon, and then to recollect that at new or old moon the earth is "full" as seen from our satellite, and that a full earth must give some fourteen times as much light as a full moon, in order to realize the brilliancy of an earth-lit night upon the moon. As the moon waxes to us, the earth wanes to the moon, and vice versa, and so the phenomenon of earth-shine on the lunar surface must be looked for before the first quarter and after the last quarter of the moon. ”

“ The zodiacal light also, which in our English latitude and climate is but rarely seen and in more favourable 161 climes appears only when the sun itself is hidden beneath the horizon, would upon the moon be seen as a constant accompaniment to the luminary throughout his daily course across the lunar sky. The other planets would appear generally as they do to us on earth, but, never being lost in daylight, their courses among the stars could be traced with scarcely any interruption. ”

“ The lunar night would be lit by our own earth, a gigantic moon, presenting a surface more than thirteen times as large as that which the full moon offers us, and hanging almost stationary in the heavens, while [pg 129] exhibiting all the effects of rapid rotation upon its own axis. Those appendages of the sun, which only the spectroscope or the fleeting total eclipse can reveal to us, the corona, the chromosphere, and the prominences, would there be constantly visible. ”

“ But whatever the former condition of the moon may have been, its existing appearance gives it a resistless fascination, and it bears so clearly the story of a vast catastrophe sculptured on its rocky face that the thoughtful observer cannot look upon it without a feeling of awe. The gigantic character of the lunar features impresses the beholder not less than the universality of the play of destructive forces which they attest. Let us make a few comparisons. Take the lunar crater called “Tycho”, which is a typical example of its kind. ”

“ Yes, thanks to us, the inhabitants of the lunar hemisphere turned toward us are gratified by the sight of a [Pg 255] splendid nocturnal torch, doubtless less white than our own despite the clouds with which the terrestrial globe is studded, and shaded in a tender tone of bluish emerald-green. The royal orb of their long nights, the Earth, gives them moonlight of unparalleled beauty, and we may say without false modesty that our presence in the lunar sky must produce marvelous and absolutely fairy-like effects. ”

“ However, after all, the time during which men have studied the moon with the telescope—only two hundred and sixty-nine years—is a mere instant compared with the long periods during which the moon has been exposed to the sun's intense heat by day and a more than arctic intensity of cold by night. It may well be that, though lunar landslips occur at short intervals of time, these intervals are only short when compared with those periods, hundreds of millions of years long, of which we had to speak a little while ago. ”