Solar System
the sun and all the bodies, by whatever name they may be called, which periodically revolve round the sun as a center. Visible to us are seven distinct orders or systems of revolving worlds. They are the zodiacal light, whatever that may be, the planetary, the satellitic, the meteoric, the cometary, the stellar, and the nebular systems. All but the latter two belong to our solar system. The limits of the planetary system, as far as known, are Mercury, the nearest to the sun, and Neptune, the most distant. This limit does not include SOLBERG rings, which, while the earth is passing through them, produce the star showers.
Every member of the solar system, be it planet, satellite, meteoroid or comet, moves in an orbit called an ellipse, of greater or lesser eccentricity. There is not a heavenly body known to man that moves in a circle. The planets and satellites revolve in elliptic orbits, while the comets move some in elliptic and others in parabolic and hyperbolic orbits. Those moving in either of the latter two can never return, as the two branches of their paths do not meet to form a closed curve as does the ellipse. For adopting the ellipse instead of the circle for planetary revolution the world is indebted to the genius of Kepler, who by the first of his three laws brought harmony out of confusion. The three laws of Kepler, as enunciated by him, are: (1) The planets move in ellipses, having the sun in one of the foci. (2) The radius vector of each planet describes equal areas PRINCIPAL ELEMENTS OF THE SOLAR SYSTEM Mean distance from sun (millions of miles) Period of revolution (days) Planet Diameter (miles) Density (earth's 1) Mass (earth's 1) Mercury 2,770 0.56 Venus 7,700 0.82 0.024 0.82 35.7 88 67.2 225 Earth 7,918 1.00 1 92.9 365 Planetoid Eros 20 ? ? 135.1 643 Mars 4,230 0.71 0.105 141.5 687 Planetoid Ceres 480 ? ? 257.1 1,681 Jupiter 86,500 0.24 318 483.3 4,333 Saturn 73,000 0.13 93 886.0 10,759 Uranus 31,900 0.22 15 1,781.9 30,688 Neptune 34,800 0.20 17 2,791.6 60,181 the hypothetical intra-Mercurial planets, discovered during the total solar eclipses, in 1878, by Watson and Swift. Its cometary extent is not known, and never will be, as several comets have computed periods of over
1,000,000 years, and even their aphelia reach only a step toward even the nearest star. The sun's far-reaching power, of course, extends to half way to the stars, and it is not an unreasonable supposition to suppose that there are comets whose aphelia extend that far, and if so, their periodic times must be several million years.
The bodies as far as known that are denizens of our solar system are the sun (the center), the planets of Mercury, Venus, earth with one satellite, Mars with 2 satellites, 428 asteroids, Jupiter and 5 satellites, Saturn with 5 rings and 8 satellites, Uranus with 4, and Neptune with 1, also Halley's, Pons', and Olbers' comets of long period, and about 25 of short period, ranging from 3.3 years (Encke's) to 13.78 years, commonly, but unjustly, called Tuttle's comet. It was discovered by Méchain in 1790. To the list must be added 200 or more meteoric in equal times. (3) The squares of their periodic times are proportional to the cubes of their mean distances from the sun. As all heavenly bodies hang suspended on nothing throughout all space each being attracted by all the others it results that they must move, and, while the motions of the planets are easily noticeable in a few hours, and even min utes, it requires to detect motion in the stars long-continued observation with instruments of great delicacy and power to ascertain that they have any motion at all, so far away are they. No planet whose orbit is interior to the earth's can ever assume the crescent phase, or rise when the sun sets, or be on the meridian at midnight, or transit the sun. On the other hand, those whose orbits are exterior to ours can never assume the crescent and half-moon phase, and are the only ones that can ever be in opposition, rising at sunset.