Imágenes de página

is become a partaker of the length and breadth, the depth and height, of divine love.

The orbit of the Earth is placed between those of Venus and Mars. The diameter of the Earth is 7970 miles; its distance from the sun is 96 millions of miles, and goes round him in a year, or 365 days, 6 hours, 9 minutes; moving at the rate of 68,856 miles per hour. Its apparent diameter, as seen from the sun, is about 21 seconds.

It turns round its axis from west to east in 24 hours, which occasions the apparent diurnal motion of the sun, and all the heavenly bodies round it, from east to west in the same time; it is of course the cause of their rising and setting, of day and night.

The axis of the Earth is inclined 23. degrees to the plane of its orbit, and keeps in a direction paral-, lel to itself throughout its annual course, which causes the returns of spring and summer, autumn and winter. Thus his diurnal motion gives us the grateful vicissitude of night and day, and his annual motion the regular succession of seasons,


Next to the sun, the Moon is the most splendid and shining globe in the heavens, the satellite, or inseparable companion of the earth. By dissipating, in some measure, the darkness and horrors of the night, subdividing the year

into months, and regulating the flux and reflux of the sea, she not only

becomes a pleasing, but a welcome object; an object affording much for speculation to the contemplative mind, of real use to the navigator, the traveller, and the husbandman. The Hebrews, the Greeks, the Romans, and, in general, all the ancients, used to assemble at the time of new moon, to discharge the duties of piety and gratitude for its manifold uses.

That the moon appears so much larger than the other planets, is owing to her vicinity to us; for, to a spectator in the sun she would be scarcely visible, without the assistance of a telescope. Her distance is but small from us, when compared with that of the other heavenly bodies; for among these, the least absolute distance, when put down in numbers, will appear great, and the smallest magnitude immense.

The Moon is 2161 miles in diameter; her bulk is about of the earth's; her distance from the centre of the earth 240,000 miles; she goes round her orbit in 27 days, 7 hours, 43 minutes, moving at the rate of 2299 miles per hour. The time in going round the earth, reckoning from change to change, is 29 days, 12 hours, 44 minutes. Her apparent diameter, at a mean distance from the earth, is 31' 16"; but as viewed from the sun, at a mean distance about 6".

Her orbit is inclined to the ecliptic, in an angle of five degrees, 18 minutes, cutting it in two points, which are diametrically opposite to each other; these points are called her nodes. Her nodes have a motion westward, or contrary to the order of the signs, making a complete revolution in about 19 years; in which

time each node returns to that point of the ecliptic whence it before receded.

If the moon were a body possessing native light, we should not perceive any diversity of appearance; but, as she shines entirely by light received from the sun, and reflected by her surface, it follows, that, according to the situation of the beholder with respect to the illuminated part, he will see more or less of her reflected beams; for only one-half of a globe can be enlightened at once.

Hence, while she is making her revolution round the heavens, she undergoes great changes in her appearance. She is sometimes in our meridian at midnight, and, therefore, in that part of the heavens which is opposite to the sun: in this situation she appears as a complete circle, and it is said to be full

As she moves eastward, she becomes deficient on the west side, and in about 7 days comes to the meridian at about six in the morning, having the appearance of a semicircle, with the convex side turned towards the sun ; in this state, her appearance is called the half moon. Moving on still eastward, she becomes more deficient on the west, and has the form of a crescent, with the convex side turned towards the sun; this crescent becomes continually more slender, till about fourteen days after the full moon, she is so near the sun that she cannot be seen, on account of his great splendor. About four days after this disappearance, she is seen in the evening a little to the eastward of the sun, in the form of a fine crescent, with the convex side turned from the sun;


moving still to the eastward, the crescent becomes more full; and, when the Moon comes to the meridian, about six in the evening, she has again the appearance of a bright semicircle: advancing still to the eastward, she becomes fuller on the east side; at last, in about 29 days, she is again opposite to the sun, and again full. It frequently happens that the Moon is eclipsed when at the full; and that the sun is eclipsed some time between the disappearance of the Moon in the morning on the west side of the sun, and her appearance in the evening on the east side of the sun. The nature of these phenomena will be more fully considered, when we come to treat particularly of eclipses.

In every revolution of the Moon about the earth, she turns once round upon her axis, and therefore always presents to us the same face; and as, during her course round the earth, the sun enlightens successively every part of her globe only once, consequently she has but one day in all that time, and her day and night together are as long as our lunar month. As we see only one side of the Moon, we are therefore invisible to the inhabitants on the

opposite side, without they take a journey to that side which is next to us; for which purpose some of them must travel more than 1500 miles.

As the Moon illuminates the earth by a light reflected from the sun, she is reciprocally enlightened, but in a much greater degree by the earth, for the surface is above thirteen times greater than that of the Moon; and, therefore, supposing their power


[ocr errors]

reflecting light to be equal, the earth will reflect thirteen times more light on the Moon than she receives from it. When it is what we call New Moon, we shall appear as a Full Moon to the Lunarians; as it increases in light to us, ours will decrease to them; in a word, our earth will exhibit to them the same phases as she does to us.

We have already observed, that from one half of the Moon the earth is never seen; from the middle of the other half, it is always seen over head, turning round almost thirty times as quick as the Moon does. To her inhabitants the earth seems to be the fargest body in the universe; about thirteen times as large to them, as she does to us. As the earth turns round its axis, the several continents and islands appear to the Lunarians as so many spots of different fo:ms; by these spots they may determine the time of the earth's diurnal motion ; by these spots, they may perhaps measure their time; they cannot have a better dial.


Mars, Jupiter, Saturn, and the Georgium Sidus, are called superior planets, because they are higher in the system, or farther from the centre of it than the earth is.

They exhibit several phenomena, which are very different from those of Mercury and Venus; among other things, they come to our meridian both at noon and midnight, and are never seen crossing the sun's disc.

« AnteriorContinuar »