“The moon,” says Dr. O. Gregory, “is a dark, or opake body, shining principally with the light she receives from the sun. If she shone by a light of her own, we should feel a sensible warmth from her rays; but it is a light reflected from the sun with which she shines, and is so exceedingly weak and languid, that the greatest burning glass will not collect enough to make any sensible degree of heat. This has been accounted for, and those who have gone through the computation assert that the light of the full moon is ninety thousand times less than day-light.” The ancients early discovered, that the moon had no light of its own, but shone with that which it reflected from the sun. This, after Thales, was the sentiment of Anaxagoras and Empedocles, who thence accounted not only for the mildness of its splendor, but the imperceptibility of its heat, which our experiments confirm.
In the Hebrew language the moon is called ירה Yarah, or, more strictly speaking, says Parkhurst, the lunar light, or flux of light, reflected from the moon’s body, or orb. That this is the true sense of the word is evident from several passages of Scripture, one of which is, “For the precious (produce) נרש ירחים put forth by—what? Not the orbs of the moon surely (for the orb is but one), but by the fluxes or streams of light reflected from it, which are not only several but various, according to the moon’s different phases and aspects in regard to the sun and the earth. And this may lead us to the radical idea of the word ירח; for as יחר and אחר, יחד and אתד &c., are very nearly related to each other respectively, so likewise I conjecture that ירח is to ארה, in sense as well as in sound, and consequently that it signifies to go in a track or in a constant customary road or way; and this affords us a good descriptive name of the lunar light; for, Behold, says Bildad in Job, chap. xxv, 5, even to the ירח or lunar light ולא יאהיל and he (God) hath not pitched a tent (for it); as he has for the שמש or solar light. No! The lunar stream has fixed station from whence it issues, but together with the orb which reflects it, and which like a human traveller moves now a quicker, now a slower pace, is continually performing its appointed journey, and proceeding in a constant, though regularly irregular track.”
The Greeks called the moon μηνη, which may be considered as a derivative from μην. Parkhurst says, This word may be derived either from μηνη, the moon, by the phases of which the month is reckoned, or else it may be deduced from the Hebrew מנה manah, to number, compute, as being computed by the lunar phases. And it is probable that the first computations of time were made by the revolutions of the moon. It is obvious to remark, that not only these two Greek words, but also the Latin mensis, a month, and the English moon, month, are ultimately derived from the same Hebrew מנה. Leigh observes, that “the Hebrews call the moon and a month by the same name, because the moon is renewed every month. The Greeks also call σεληνη, from σελας, because it every day renews its light.” Parkhurst on the word σεληνη says, “The Greek etymologists, and particularly Plato, deduce it from σελας νεον, new light, because its light is continually renewed.” But the learned Goguet says; “The Greeks gave to the moon the name selene, which comes from the Phœnician word (לן or לון namely) which signifies to pass the night; whence also we may observe is plainly derived the Latin name of the moon, luna.” From lun with the termination a, comes luna, and this name is given to the planet from her changing or appearing under different phases.
As to the dimensions of the moon, according to the most accurate calculations, her diameter is 2,175 miles, the circumference 6,831 miles, the surface contains 14,898,750 square miles, and its solidity 5,408,246,000 cubical ones. Her bulk is equal to about a fiftieth part of our earth, and her mean distance from the earth is about 240,000 miles.
The motions of the moon are most of them very irregular. The only equable motion she has, is her revolution on her own axis. The time in which she moves round her axis is about 27 days, 7 hours, 43 minutes, 5 seconds; and her revolution through an elliptical orbit is performed in the same time as her rotation on her axis, moving about 2,290 miles every hour. Her revolution round her axis exactly in the same time that she goes round the earth, is the reason she always turns the same face towards us: she has only one day and one night in the course of a month. From a long series of observations, it has been ascertained that the moon makes a complete revolution in 27 days, 7 hours, 43 minutes, 5 seconds; this is called the periodical month; but, if we refer to the time passed from new moon to new moon again, the month consists of 29 days, 12 hours, and 44 minutes, which is called the synodical month. This difference is occasioned by the earth’s annual motion in its orbit. Thus, if the earth had no motion, the moon would make a complete round in 27 days, 7 hours, 43 minutes, and 5 seconds; but while the moon is describing her journey the earth has passed through nearly a twelfth part of its orbit, which the moon must also describe before the two bodies come again into the same position that they before held with respect to the sun: this takes up so much more time as to make her synodical month equal to 29 days, 12 hours, and 44 minutes. The motions of the hour and minute hands of a watch may serve to give some idea of the periodical and synodical revolutions of the moon; for when the minute hand has performed a complete revolution, it has yet some distance to go to obtain a coincidence with the hour hand, similar to that which it had the preceding hour.
We have observed that the same face is turned towards us during the whole of the moon’s revolution, and that the other half of her surface is never visible to us. This arises from the two motions we have noticed, which, with regard to our view of the moon, appear to counteract each other. Her revolution round the earth is performed towards the east; while the revolution upon her own axis is performed towards the west: so that, one of these motions turns as much of her face from us, as the other turns towards us. And from the moon’s axis being inclined to the plane of her orbit, sometimes one of her poles is inclined towards the earth, and sometimes the other: in consequence of which, we see more or less of her polar regions in different periods of her revolution. When the moon is in perigee, or nearest distance from the earth, her motion is quickest; and when in apogee, or most remote distance, her motion is slowest.
The length of the day is equal to our lunar month, for all that time is included in one revolution round her axis. Her days and nights, therefore, will constantly be of the same length, or almost fifteen of our days each. The year will be exactly the same with our year; because, being an attendant on the earth, she must go round the sun in the same time as that does. Her difference of seasons will be much less than on our earth, having only a small inclination of her axis of six degrees and a half; so that the variation between her summer’s heat and her winter’s cold must be comparatively inconsiderable. Hence there will be only thirteen degrees of Torrid Zone, on some parts most opposite the sun, and thirteen degrees of Frigid Zone on those contiguous to her poles; which consequently must leave seventy-seven degrees for what we should call her Temperate Zones, both in the north and south parts from her Equator. Our earth, unquestionably, performs the office of a moon to the moon, waxing and waning regularly, but appearing thirteen times as large, and, of course, affording her thirteen times as much light as she does to us. When she changes to us, the earth appears full to her; when she is in her first quarter to us, the earth is in its third quarter to her; and vice versâ. To the moon the earth seems to be the largest body in the universe, and must indeed be a most magnificent sight.
On the supposition that the moon is inhabited, it may be observed, that those who are placed about the middle of the surface, or face next to us, will constantly see our earth over their heads, and increasing and decreasing in light, like as the moon itself appears to us. Those who are situated near the borders, whether on the right or left, or upon the top or bottom, will also constantly have the same appearance in the opposite part of the horizon. But those who live on the side of the moon which is not presented to us, will know nothing of our earth, or at least, they will never have an opportunity of seeing this large and wonderful moon, without travelling perhaps more than 1,500 of our miles on the surface of that luminary. To those who live on this side of the moon, or travel to it on any account, as we may pass from the northern into the southern hemisphere of our globe, the earth, indeed, when at full to them, will appear to be more than three times as broad as the moon does to us, and to communicate, as has been already mentioned, about thirteen times as much light to her, as she does to us when at the full.
The moon, possessing no native light, shines entirely by light received from the sun, and which is reflected to us from her surface. That half of her which is towards the sun is enlightened, and the other half is dark and invisible: hence, when she is between us and the sun, she disappears, because her dark side is then towards us. Whilst making her revolution round the heavens, she undergoes a continual change of appearance. She is sometimes on our meridian at midnight, and therefore in that part of the heavens which is opposite to the sun; when she appears with a face completely circular, which is called a full moon. As she moves eastward, a part of her dark side comes forward on the western side, and, in a little more than seven days, reaches to the meridian, at about six in the morning, having the appearance of a semi-circle, with the convex side turned towards the sun: this crescent gradually becomes more slender, till, about fourteen days after the full moon, being so near the sun, and in a line between that luminary and our earth, she is rendered invisible to us, from the superior splendor of that orb of light. About four days after this disappearance, she may be seen in the evening, a little to the eastward of the sun, in the form of a fine crescent,[121] as before, but having her convex side turned from the sun. Travelling still towards the east, the crescent becomes wider; and when advanced to the meridian, about six in the evening, she again bears the appearance of a bright semi-circle, with the same difference that we observed of the crescent, that is, its convex side is now turned from the sun. Advancing still more eastward, the semi-circular moon widens into an oval shape, till at last, in about twenty-nine days and a half from the last opposition to the sun, she is again in the same situation, and appears a full moon.
The following account of the harvest moon, so called, taken from the Pantalogia, will no doubt be acceptable to the reader.—It is remarkable that the moon, during the week in which she is full about the time of harvest, rises sooner after sun-setting than she does in any other full moon week in the year. By this means, she affords an immediate supply of light after sun-set, which is very beneficial for the harvest and gathering in the fruits of the earth; and hence this full moon is distinguished from all the others in the year, by calling it the harvest-moon.