ASTRONOMY.

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height ; and having contracted telescope? far more powerful thanany former ones, proceeded to other observations; such as, on therotation of the planets round their axes; on the parallax of the'fixed stars; catalogues of double, triple, &c. stars; on the pro-sper motion of the >uu and solar system ; on the remarkable ap-pearances of the polar regions of the planet Mars , &c. March 1.1th,

1 TS1, he discovered a new planet at about tw ice the distance of Su-tir.n from the sun; he called it the Georgian Planet, but foreign astro-nomers named it, the Hersclnd ; and by some it is denominatedT . anus. Since that time he discovered the six satellites of this newplanet, and two belonging to Saturn which had not been beforeobserved.

(36.) On the first day of the present century a new small planetcalled Ceres Ferdinandea , was discovered by Mr. Piazzi, an Italianastronomer, and another called Falla-;, on the CS-th of March,1S02, by Dr. Olbers , of Bremen. After which, Mr. Hardingmaking his observations at Lilienthal, discovered on the 1st ofSeptember, ISO-1, a third small planet, called Juno; and a fourthwas found out on the ?9th of March, 1807 by the indefatigableastronomer, Dr. OlbeTs, who first ohserved the planet Pallas. Thishe has named Vesta.

(37.) Historical accounts and lists of the principal authors and writ-ings on this science, are contained in We.-dlcr’s and Bailly’s His-tory of Astronomy, Adam, Vossius, Bayle, Chanffepie, Nic.eron,Perraut, the chronological table of Riccioli, and that of Sherburn,at the end of his edition of Manilius ; and the first volume of DeLa Lande’sastronomy, may also he consulted, The more modernand popular books on astronomy are very numerous, and wellknown; as those of Ferguson, Long, Emerson, Vinee, De LaLande, Leadbetter, Brent, Keil, Winston, Wing, Street, Bonny-eastle M. dela Place, Ac. &e.

PART I.

Of the Systems of Astronomy, and the Appearancesof the Celestial Bodies .

Sect I. Of the most obvious Celestial Phenomena.

(3S.) Every one must have observed the daily rising of the suitin the east, and his setting in the w est; as also that of the moonand stars appearing and keeping the same w esterly course. Butneither the sun nor moon always rises exactly in the same pointof the heavens. If we observe the sun, from the beginning ofMarch, we find that he seems to rise almost every day sensiblymore to the northward, than he did the day before, to continuelonger above the horizon, and to be more elevated at mid-day,till towards the end of June, when he is observed to move south-ward in the same manner, till near the end of December, when hebegins again to move northward, and so on.

(39.) When the new moon first becomes visible, she appears inthe western part of the heavens, near tlie sun. Every night sheincreases in size, and removes to a greater distance from the sun,till at last she appears in the eastern part of the horizon, just atthe time the sun disappears in the western. After this she gradu-ally moves farther eastward, rising every night somewhat later,till at last she seems to approach the sun a« nearly in the east asshe did in the west, and rises only a little before him in the morn-ing, as in the first part of her course she set in the west not long’after him. All these different appearances are completed in thespace of a month; alter which they begin in the same order asbefore.

(40.) The stars seem to turn round two immoveable points,near one of which, in the north, is placed a single star called tin-pole, or pole-star. This point is more or less elevated accordingto the different parts-of the earth from which we take our view.The inhabitants of Lapland , for instance, see it much more ele-vated above the horizon than we do ; we see it more elevated thanthe inhabitants of Spain ; and they, again, see it more elevatedthan the inhabitants of Barbarv. By continually travelling south,this star at last appears on the horizon, and the other pole just he-roines visible on the opposite point of the horizon. A straightline connecting these points is called the axis, round which, asa fixed line, the whole heavens apparently revolve, once in 23hours, 56 minutes, and4 seconds.

(41.) A few of the stars are observed to change their places withregard to one another, or to any fixed point in the heavens.These, denominated planets, (from nUe.nw, to wander,) are, Mer-

cury ( $ ), Venus ( 5 ), Mars (<f ), Ceres Ferdinandea , Pallas, Juno,Vesta, Jupiter (![), Saturn (1?), and Herschel ($), ortheGeor-gium Sides. About Jupiter four bodies, called moons, secondaryplanets, or satellites, are observed to revolve. The Earth lias one ;Saturn seven; and the 1 lerscliel six such moons.

(42.) There are besides the planets, other bodies which varytheir situations, appearing for a short time, and most of them atuncertain intervals; their number is supposed to exceed 450.They are called comets, from xogaim;, hairy, having generally along tail, somewhat resembling the appearance of hair.

(43.) The remaining stars, called fixed, keep the same positionwith respect to one another, and are further distinguished fromthe planets by their twinkling.

(44.) In order to ascertain for any given time the places of thecelestial bodies, and to distinguish their relative situations, astro-nomers have conceived various points and circles in the sphereas generated hv the apparent motion. The principal of these it is pro-per now to explain, the rest will he described in the course of thiswork. In Fig. 10, Plate XXV. .let zorh represent the earth, andZOltH the heavens at an immense distance. Great circles aresuch as cut the sphere into two equal parts, less circles into twounequal parts, and every circle is conceived to be divided into360 degrees. The point in the heavens, or among' the stars, direct-ly over any place, is the zenith of that place, and the oppositepoint is the nadir; thus Z is the zenith, and N the nadir to theplace ;, which suppose London . The great circle w hich is 90 1 *from the zenith or nadir, or exactly in the middle between them,is termed the true or rational horizon, as HO, or ho under it onthe earth. The line, which terminates the view on every side, isthe sensible or visible horizon, which is parcllel to the true, andvaries according to the altitude of the eye ; when tiie eye is ill the•surface of the sphere as at z, this horizon is but as a point on theearth; hut in the heavens it is represented by MR, and coincidesv’ith the true, the arc RO, or Mil, equal to the earth’s semidia-meter, being imperceptible on account of the great distance of thestars. When the eye is more elevated as at m, a greater portion ofthe earth’s surface presents itself, as is shewn by the tangents m l,mr, but in the heavens this termination is below the true horizon,as VL ; the depression is measured by the angle R l L, or M v V,which is called the dip. It is in this circle that the celestial bodiesrise and set. It is evident that every different place has a differ-ent zenith, nadir, and horizon. The cardinal or principal points ofthe horizon are the east, west, north, and south, dividing it intofour quarters. In the starry heavens two points are ohserved toremain constantly at rest, these are named the poles; and l’S con-necting them is the axis, round which, once every day, the sun,moon, stars, planets, and comets, revolve, apparently in circles,whose planes are perpendicular to the axis; this is called the diur-nal motion. Of these circles, that which is in the middle betweenthe two poles is a great circle, as EQ, called the equinoctial, andthe circle under it on the earth eq is the equator; the olhei circlesare parallels of declination, as FA, or ZY, and those answeringto them on the earth, as./h, or zy, are parallels of latitude. Thesun’s annual motion is in a great circle cutting the equinoctial inan angle of M-p- degrees, and is called the ecliptic, as '1 A. 'Phis isdivided into twelve signs of 30° each, named and marked thus-:Aries Gy), Taurus (B), Gemini (n), Cancer (©), Leo (SL),Virgo (lljj), Libra (=^), Scorpio (Iff), Sagittarius (f ), Capricor-nus (vj 1 ), Aquarius (CC7), Pisces (X). When the sun is in the intersec-tion of the ecliptic, and equinoctial, or the equinoctial point, his di-urnal motion is in the equinoctial, but when he has arrived at T, hisutmost limit northward,his diurnal motionisiin the parallel TA,calledthe tropic of Cancer, when at A, he describes the tropic of Ca-pricorn AF; the tropics are 23 degrees from the equinoctial; atthe same distance from the poles are the parallels BG and K.Xcalled polar circles ; the northern is the Arctic , and the southern theAntarctic circle. The tropics and polar circles on the earth divideit into five zones, two Jrigid, two temperate, and one torrid.When the sun is at T,and describes the tropic TD, he will be verti-cal in the course of that dav, or revolution, to all places on theterrestrial tropic t d ; when he is at l', he w ill he over a, inlike manner us when at T, he is over the point t. When he isin any other point of the ecliptic as at J, and describes the paral-lel of declination 1W, he will be vertical to a like parallel of latj-tude, as ij ze. Great circles passing through the poles and zenith,as PZES, PJS , and PUS are called, meridians, as are those di-9 rectly