SOLAR SYSTEM, that collection of bodies of which the earth on which we dwell is one, and which are distinguished from all other bodies in the universe by having the sun as the centre of their motions. The bodies of this system may be classified as follows: 1. The Sun.— The great central body, shed ding its light and heat on all the other bodies and by its powerful attraction, keeping them in their several orbits. It is the fountain-head of all life on the earth. It is about 750 times as massive as all the other bodies of the system put together; hence its attractive power on all these bodies. For a full description of this great luminary, see Susi.
2. The Planets.—Bodies which revolve round the sun in elliptic orbits, generally differing little from circles. The planets are opaque and are, therefore, visible to us only by reflecting the light of the sun. They are divided into two classes, major and minor planets.
The major planets are eight in number; their names, distances and many other particu lars respecting them will be found in the table appended to this article. It will be seen that the most distant, Neptune, is more than 70 times as far from the sun as the nearest, Mercury. An idea of the arrangement of the planets will be gathered from the accompanying plate.
It will be noticed by the plate that there is a gap between the orbits of Mars and Jupiter. This is filled by the second class of planets, called minor planets or asteroids. These bodies are much smaller than the major planed and generally revolve in more eccentric orbits. It is impossible to say exactly how numerous they may be; more than 800 are now known, new ones constantly being discovered, and there may be hundreds, or even thousands, so small that they have not been discovered, and may never be separately recognized. See ASTEROIDS.
3. The Satellites of the Planets.— All the major planets, with the exception of the two inner ones, have one or more smaller bodies revolving round them and accompanying them in their courses round the sun. In this respect each of the planets having satellites may be said to form a solar system in miniature, since the motion of the satellites round the planet is quite similar to that of the latter round the sun. The number of satellites is as follows:
There are, therefore, 27 satellites now known. The system formed by a planet and its satellites is designated by the name of the Janet. Thus we have the Martian System, the Jovian System, the Saturnian System, etc.
4. Comets.— Comets generally revolve in orbits so eccentric that, during the greater part of their course, they are entirely invisible, even to telescopic vision. A few are known to revolve within the orbit of Jupiter, and all that we can observe must have their perihelion not more than two or three times as far as the earth's orbit — otherwise they would be for ever invisible. Their times of revolution vary all the way from three years to unknown thou sands of years. Those having long periods far beyond the orbit of Neptune during their course. No limit can be set to their number. Kepler's remark that the heavens may be as full of comets as the sea of fish, though prob ably an exaggeration, is well fitted to give an idea of the possible number of these bodies. It is certain that only an insignificant fraction of the total number has ever been seen by human eye. See COMETS.
S. Meteorites or Meteors, which must be countless millions of millions in number, are so minute that we never see them individually except when they strike our atmosphere and form a shooting star. (See SHOOTING STARS). They may be classed with comets, because the latter are probably of meteoric constitution; perhaps made up of meteors.
6. The Zodiacal Light, which is a great lens shaped cloud of small particles surrounding the sun and extending nearly to the orbit of the planet Mars. This cloud is thickest at the sun, but has a region of reversed curvature within the orbit of Mercury. Its form may be quite closely represented by two ellipsoids of revolu tion, having the centre of the sun for their common centre, the eccentricity of the inner being about 0.2a, and the outer having the form• of a thin, ellipsoidal sheet, within which the innermost planets are immersed.