Слике страница
PDF
ePub

Heographers divide the surface of the earth, to be er tended to the heavens po that the whole circumference of the horizon of the heavens is supposed to be $60) de. greex, or proportional parto, hall is 180 degreer, and quarter is 90 degrees. And as we see one-half of the heavens above the horizon, it is of course 180 degrees from one side of the horizon, in a line passing over uw heads, to the side directly opposite and of course from the point over our heads, called the senses, it is 90 de greer to the horizon on every side.

Remember, then, that the whole heavens are 900 de. grees, or proportional parts round, and that from the point directly over head, it is always 90 of these degrees down to the horison.

An observer of the heavens will discover the progres. sion of the whole, from east to weet, by a quarter of an hour's attention. Let him bring a sfar, in any part be tween the senith and the southern part of the horizon into apparent contact with the end of a house, steeple or other fixed object, and he will in a few minutes per crive the motion of that star, and of the whole heavens, from east to west.

It may be proper for the student now to consider, that this geveral motion of the whole heavens is merely appa rent and is occasioned by the rotation of the earth on Its aris in a contrary direction. Of course, if the pece tator is moving on the earth from went to east, the die tant stars will appear to move from east to west.

"The rising and setting of all the distant henvenly boa dies will, hence, be easily understood. The earth form completely round every twenty-four hours! every inhabitant of it will, therefore, be carried round towants all the bodies out of it, and distant from it, every twenty four hours. Hence, the rising and setting of the Sun the succession of day and night and all the dependent phenomena

This progression of the whole heavens from case to wort: the rising of some stars in the past, and the section of others in the went are ohjecte which, vieweit in this manner, will leave impressions enuch stronger than the mimic representation of the same phenomena on the even Jestial globe. The immensity of the great vnúlt of honven, the still, solemn, anisorin motion; the accompanying Association of the immeasurable distances, the apparent perpetuity, and the countless numbers of the stars, will all ibe mind with reverence and devotion towards the omuipotent, iufiuite, and eternal Author of the Whole!

Having thus obtained ocular demonstration of the motion of the stars from east to west, or rather of the motion of the earth in the contrary direction, it will then be necessary to attend to another circumstance which is a consequence of that motion.

A slight consideration will evince, that the stars imme diately above the axis on which the carth may be sup posed to turn, will appear to remain stationary over those places, at both ends of the axis. In turning wheel on a 6xed axis, all the parts of the circumference will successively present themselves to different objects but the axis will continue to point to the same place If the wheel be supposed to be a globe revolving on a aris, the effect will be the same : the point of the axis, called the pole of the globe, will point to the same spot, whila all the parts will perform smaller or larger ciri cuits in proportion as they are removed in a greater of less degree from the poles.

It is important, then, to be able to determine the points in the heavens which are opposite to the poles o. the earth, these always appear to stand still, while the older stars appear to make a daily circuit round them. Aw however, voe can only see 90 degrees in the heavens from the point over our oron heads, the inhabitants of no part of the earth can see both poles, except those who live at the equator, from which both poles are distant ninety degrees. "The poles of the heavens may therefore be seen at the equntor, exactly in the horizon, in the north and the south; but if you travel or sail one degree to the north of the equator, 80 as to be within 89 degrees of the north pole, you will, of course, see one degree beyond the north pole, and not so far as the south pole by one degree: because, as before stated, you can always see 90 degrees in the heavens, from your Zenith,

of place over head, In England, which lies between 50 and 60 degrees from the equator, or within 10 or 50 des greea of the north pole, we always see 50 or 60 degrees heyand or below the north pole i or, in other words, the north pole in the heavens, or the stars immediately over the north pole of the earth, will be 50 or 60 de. grees high,

Nather above mid way between the horizon and the wenith, in this northern part of the heavens, we who are in England must look for the north pole of the heavens, or the part which never appears to move, it happens that there is a star so near the morih pole, that for all ordinary purposes it may be taken for the north pole itself; and this star may alway, he found very easily, hy means of two other stars which point to it in a right line, During the winter months, these stars, which are in the constellation of the Great Rear, are to be found with the other bars of that remarkable constellation, on the eastern side of the pole. They are about six degrees anunder, and the nearest is five times that space, or thirty degrees from the polar atar, at which they seem to point, and are, thence, called the Painters,

The worth pole sar being thus found, it will be a pleasing employment to observe, that all the stars appear to move found it, according to their several distances, while it constantly standa still, An hour's contemplation of this star, and of the motions of the rest of the heavens, while it remains and immo eahle centre, will teach more to the uniformed in astronomy, than a thousand lessons or lectures in the closet,

On a winter's evening, the other remarkable objects in view, will be the biasex, or seven stars, in the southeast, and below them, a little to the east, the grand constellation of Orion : audi still lower, the dangstar Sirius, the brightent of all the fived atars, The three bright stans together in a line, called the Reit of Orion, are at about equal distances from the Headles and fyrius that in, about twenty five degrees from each. Desides remembers ing this distance, and that of the Pointers, before-mentioned, for the sake of nocasional comparisons, it will bo useful to recolleet, that the most northern of the three dar in the Belt of Orlon, in exnctly over the equator so that from that star to the north pole war is exactly pinety degrees.

The Pl'lades are in the Zodiac, on the south side, and 10 is the red star Aldeberan, near them; and the two bright stars about forty degrees to the left, called Castor And Poliur, or the Twins, are also in the Zodiac, and about five degrees north of the Sun's place, on the 19th of July.

On such an evening, the Milky Way will be seen in the west, us a light cloud : supposed by some to be formed of a mass or shoal of stars, almost infinite in number, but indistinct from their distance, though others suppose it to consist of a lumipong space, and not of Atarı.

A celestial globe, rectified to the day and hour, will point to other objectx , an ephemeris will indicate the names or places of the planets which may then be above the horizon; and any telescope will render visible many other interesting and wonderful phenomicon.

Should the Moon be visible, the motion in her orbit may be nightly traced by her approximating to, or receding from, certain stars, and the same may be obe served in the motion of the planets in their orbits.

The morning and evening stars are the bright planets, Venus and Jupiter, ro called from their rising or setting with the Sun. Mars is red: Saturn of a leaden colour Herschel is so distant, and Mercury in so near the Sun, that they can seldum be seen but with a telescope.

[merged small][graphic]
[ocr errors]

Very amall telescopes will shew most of the celestial phenomena s Jupiter's moons, Saturn's ring, the moonlike phases of Veous, tho Pleiades, the luninous space in the sword of Orion, the Spots in the Sun, and the mountains in the Moon, may all be seen with such telescopes as are bought for ten or 'fifteeu shillings. Calileo made all his great discoveries with a telescope cight or ten inches long, and which magnified only ten or (welve times,

JUPITER, HIS MOONS AND BELTS.

[graphic]
« ПретходнаНастави »