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SOLAR SYSTEM
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See also:SOLAR See also:SYSTEM , in See also:astronomy, the See also:group of heavenly bodies, comprising the See also:sun and the bodies which move around the sun as a. centre of attraction, of which the See also:Earth is one. These bodies may be classified as follows: first the Sun, 0, distinguished as containing much the greater See also:part of all the See also:matter composing the system, being. more than 600 times as massive as all the other bodies combined. It is this See also:great See also:mass which makes it the central one of the system. It is also, so far as is known, the only incandescent See also:body of the system, and therefore the only one that shines by its. own See also:light. Secondly, See also:planets. The bodies of this class consist of eight See also:major planets moving See also:round the sun at various distances, and of an unknown number of See also:minor planets, much smaller than the major planets, forming a See also:separate group. Thirdly, satellites., or secondary planets revolving around the major planets, and therefore accompanying them in their revolutions around the sun. A See also:fourth class of bodies, the constitution of which is still in some doubt, comprises comets and meteors. These differ in that comets are visible either in a See also:telescope or to the naked See also:eye, and seem to be either. wholly or partially of a nebulous or gaseous See also:character, while meteors are, individually , at least, invisible to us except as they become incandescent by striking the See also:atmosphere of the earth. It is, however, an open question whether a See also:comet is other than an See also:accumulation of meteoric bodies (see COMET). The major planets are separated into two See also:groups of four each, between which the minor planets, for the most part, revolve. The arrangement of the major planets, with the. See also:numbers of their respective satellites thus far known, in the See also:order of distance from the sun, is as follows: The first group in order—the smaller major planetscomprises:- See also:Mercury, , with no known See also:satellite; See also:Venus, ?, with no known satellite; The Earth, ®, with one satellite, the See also:moon; See also:Mars, d', with two satellites. Outside of this group lies the See also:zone of minor planets or asteroids. The See also:outer group of major planets comprises: See also:Jupiter, with eight satellites; See also:Saturn, h, with ten satellites; See also:Uranus, or gt, with four satellites; See also:Neptune, with one satellite. The distances separating the individual orbits in each group seem to. approximate to a certain order of progression, expressed in See also:Bode's See also:law (see BODE). But there is an obvious See also:gap between the two groups of major planets which is filled by the group of minor planets. Taking the mean distance of this group as that of a See also:planet, the distance of the major planetsclosely approximates to Bode's law, except in the See also:case: of Neptune. A remarkable feature of the solar system, which distinguishes it from all other known systems in the universe, is the symmetry of arrangement and See also:motion of its greater bodies. All the major planets and many of the minor planets revolve in elliptic orbits so nearly circular in See also:form that the unaided eye would not See also:notice the deviation from that form. But as the orbits are not centred on the sun, which is in a See also:focus of each, the displacement of the seeming circle would be readily seen in the case of Mercury and of Mars. The same statements are true of the orbits of the satellites around their primaries. The major planets all move around the sun in the same direction, from See also:west to See also:east, in orbits but little inclined to each other. All the known minor planets have the same See also:common direction, but their orbits generally have a greater eccentricity and mutual inclination. The See also:general See also:rule is that the satellites also move round in the same direction, and in orbits of moderate inclination. Exceptions occur in the case of the satellites of Uranus, which are nearly perpendicular to the See also:plane of the See also:orbit. The satellite of Neptune, and one satellite, See also:Phoebe, of Saturn, are also quite exceptional, the direction of motion being See also:retrograde. For the elements of the orbits, and the general character of the several planets see PLANET. Details as to each are found under the respective names of the several planets. (S. Additional information and CommentsThere are no comments yet for this article.
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