Concluded from Scientific American Supplement, No. 2188, Page 368, December 8, 1917 PASSING over the minor planets for the present, we have now to consider briefly those four colossal orbs whose paths are far beyond that of Mars. They differ from the smaller major planets, not only in size, but also in constitution. They are much lighter than the smaller planets in proportion to their volume, and are in a much less solid state. Their size has probably prevented rapid cooling. They have a total of 24 moons whereas the four smaller major planets have, in all, only three moons. These four colossal planets include vast areas with.n their orbits. Neptune, the outermost, being nearly twenty times as far as Mars from the sun. The comparative areas included in their orbits is therefore almost one to four hundred. Jupiter is far the largest of the planets. (Diameter, 84,000 miles.) It is larger, indeed, than all the others combined. How appropirate that this mighty sphere should have such a name! But is it not strange that Venus, who looks so much brighter, was not in pre- statistical-days called Jupiter? Probably Venus was named first because of her greater brilliancy, and in virtue of her conspicuous beauty, received the name of the charming goddess, after which the only name worthy of the great planet we are now considering was that of the father of the gods. Jupiter resembles the sun and Saturn in the fact that he is not solid at his surface. His equatorial regions, like theirs, float somewhat freely over the deeper layers of his body. The surface at the equator completes an axial revolution in less time than is required by the polar regions to complete theirs. This may not mean that Jupiter and the sun are slackening their pace. It may be explained by centrifugal forces. Juptier's axis is perpendicular to his orbital plane, which is inclined to the ecliptic at an angle of only 1° 8". Seasons are absent from Jupiter's year, which is equal to about twelve of ours. He therefore passes eastward, as seen from earth, through about one zodiacal sign each year. The Jovian day is less than ten hours, or about twenty minutes less than the day of Saturn. Bodies weigh about two and a half times as much as on the earth and 20 per cent, more at the poles than at the equator. Jupiter and the poles of Saturn are the only places in the solar system, away from the sun itself, where bodies weigh heavier than on earth. There are 10,455 days in the Jovian year. A point at the earth's equator moves a little over 1,000 miles per hour, a similar point on Jupiter's equator moves about 26,000 miles per hour. Jupiter has nine moons. The four largest were discovered by Galileo, being among the very first objects revealed by the aid of the telescope. The latest Jovian moon was discovered in 1914 by means of the photo- plate, the object being too distant and too small to be seen with the largest telescope. This latest discovered satellite moves in an orbit whose diameter is about 32,000,000 miles. Its motion is, like that of the satellites of Uranus and Neptune, apparently retrograde. The succession of transits, occultations, eclipses, etc., of Jupiter's moons as seen from earth are among the most interesting phenomena an amateur can study and observe. The author of this paper remembers gratefully the excellent three-inch archromatic telescope through which he had a first glimpse of Jupiter and his four great moons, and has almost tender reminiscence of the little, old gentleman who so graciously afforded him that great pleasure. Interesting as the Jovian lunar phenomena are, as seen from the earth, they would be much more so if they could be viewed from the planet itself. At present we may but sigh and piously express the hope that some day all that is indestructible in death's tremendous adventure may be clothed in a body so ethereal as to defy all those chemical and physical changes which set barriers here to our complete freedom. If such a faith be well founded, and some of us think it is, we shall then see the beauties of the worlds that are now only ideal, we shall perceive the subtle forces that dwell beyond the violet rays and hear the music of the ultratonal harmonies. From the disparity between the predicted and the observed times of eclipses of Jupiter's moons, a time element was found to exist in relation to the movement of light from one part of the universe to another. Before that, light had been supposed to move to any distance instantaneously, as we have up to the present supposed gravitation to act. Even gravitation has recently been made the subject of question in relation to a time element. *Journal of the Royal Astronomical Society oj Canada. Saturn. It is about 400,000,000 miles from the orbit of the earth to that of Jupiter. Another 400,000,000 miles brings us to the orbit of Saturn, the second largest of the planets, Jupiter is 1,300 times the volume of the earth. Saturn is 770 times the same volume. The body of Saturn (diameter, 73,000 miles) is not yet rigid and its axis is inclined to the plane of its orbit at an angle of 27°. The seasons are well marked in the Saturnian year, but each quarter lasts about seven terrestrial years. Bodies weigh more at the poles of Saturn and less at the equator than on our earth. The most distinctive feature of this planet in his uni que system of ri ngs. These are in the plane of Saturn's moons, with the exception of the outermost moon which is apparently retrograde in motion. The rings consist of meteors. From the centre of the planet to the circumference of its outer ring there are, first,the 36,500 miles of the radius of Saturn. From the surface of the sphere to the inner margin of the inner rings is 9,000 miles. This, which is known as the crepe ring, is 12,500 miles in width and runs into the middle ring which is 17,000 miles wide. Outside the middle ring is a space of one thousand miles before the outer ring, 10,000 mile wide, is reached. As Saturn's orbit is inclined to the ecliptic at an angle of 2° 30' we should always see the Saturnian rings as a linear projection were it not for the inclination of his axis to the plane of his orbit. This leaning towards us of one or other of his poles shows us sometimes the north, at others the south, side of the rings and occasionally at the transition point, the linear configuration is seen. Only the most powerful telescopes will show the rings at all when they lie edgewise to the plane of our vision. Saturn has ten moons, only one of which (Titan) is larger than ours. The first four, like our own and some of the moons of Jupiter, have been proven to turn always the same surface towards their primary. As no exception to this rule has been found, it is likely that it obtains in the cases of all moons. The ninth moon of Saturn (Phoebe) has technically a retrograde motion. Uranus and Neptune. Nearly 1,000,000,000 miles beyond the path of Saturn is that lone track where Uranus runs his silent course and from which he beckons his farthest frontier signals to our unassisted vision. Thus between the orbits of Saturn and Uranus, the entire solar system as far out as Jupiter and his farthest moon might easily perform all their revolutions. The same may be said of the space between the orbits of Uranus and Neptune. These two planets might well be called the lonely worlds, since each of them is more than ten sun distances from any other planet. Uranus appears as a faint green star and is 65 times as large as the earth. The spectroscope reveals a substance in the Uranian atmosphere not known to us on earth. Uranus has four moons and Neptune one. They are all smaller than our moon. These planets and their moons were long supposed to have a retrograde motion, i.e.j the planets were supposed to rotate and the moons to revolve in a direction contrary to that usually followed by other moons and planets. It is now thought that the inclination of the planets to the plane of their orbits is more than ninety degrees and that therefor their motions follow the general rule. Technically speaking, the motions of these planets and moons are retrograde, but an interesting theory is gaining favor which claims that this was originally the direction in which all moons and planets revolved, and that the west-to-east movement was a later development. Ten pounds on earth would weigh nine on Uranus, and a few ounces less on Neptune. Neptune. The story of how Adams and LeVerrier worked out the position of Neptune mathematically before the planet had as yet been seen, basing their calculations upon the reported deviations of Uranus from his predicted course, is well known as one of the most brilliant achievements in the history of science. In such subtle manner does the human mind come into a real harmony with that unseen Force that swings the balanced worlds. Such vivid and conspicuous results of our investigations of law would almost tempt one, with Pythagoras, to strain the ear and listen for “the music of the spheres.” Like Uranus, Neptune has a far-reaching atmosphere. The Minor Planets. Beyond the orbit of Mars, yet within that of Jupiter, lie several hundreds of bodies, all of them less than 500 miles in diameter, known as the minor planets. The theory has been advanced that these are the fragments of a shattered major planet that has been broken up and scattered in detail throughout this region. The irregular shapes and motions of many of these small bodies seem to support such a theory. The presence of such a planet was long suspected in this region, a fact which lends further support to such an idea. Certain analogies as to the distances of the respective planets from the sun (Bode's Law) led a number of astronomers at the beginning of the nineteenth century to suspect the presence of an undiscovered planet between the Maritan and Jovian orbits. They instituted a methodical search, but an outsider, Piazzi of Palermo, was the first to discover a new planet. This was named named Ceres. Others were soon discovered and named after the classical godesses till such names were exhausted. Other names have since been used, but resort is now had to numbers, for over 800 of these minor planets have been discovered, catalogued, and marked on the “zodical way-bill.” They vary in diameter from a few hindred yards to about 500 miles. Only one of them, Vesta, the third largest in size, can be seen by the unaided eye, and then only under the most favorable conditions. Its diameter is about 240 miles. The orbits of the minor planets are inclined to the ecliptic variously up to 30°. They move in very eccentric orbits. Their combined volumes are not equal to more than one-fourth that of the earth, and it may be far less. Gravity on the surface of such small bodies is quite inconsiderable, and it is believed that a human arm might, even on the largest of them, cast a stone into space so forcibly that it would never return. The most interesting of all these minor planets is Eros. It is the only one within the orbit of Mars. It approaches the earth more nearly than any other planet, major or minor. Its next nearest approach will be in 1938, when it will be within 13,500,000 miles. It rotates in five and a half hours. Its diameter is probably about twenty miles. Comets and Meteors. Comets are aggregations of meteors, dust and vapor, and meteors are particles of disintegrated comets. Conets are the product of irregular or so-called accidental cosmic action. Meteors are cosmic debris resulting from attractions and repulsions that must be almost constantly active in one or other part of the heavens. The meteors are dead bodies left on the battlefields in the great war of the worlds. The breaking up of Biela's comet in 1846 is a well- known incident in the history of the subject. The comet returned in two parts widely separated in 1852, and in 1872 as a meteoric shower which was unquestionably a part of the comet. Comets and meteors are all probably of solar origin. This theory is strongly sustained by the fact that no element or substance foreign to our system has ever been found in any of these celestial adventurers. So far as has been ascertained, they all move in closed or eliptical courses. The solar system, therefore the earth's atmosphere, is moving constantly in one direction. If comets and meteors were not all of solar origin, they would assail the earth's atmosphere chiefly from that portion of the heavens which confronts it in its onward course. There would at least be a distinct preponderance of these bodies seen from that direction. But no such preponderance is found. The distinctive features of comets are thus reduced to their peculiar phenomena, and their amazingly eccentric courses. The nucleus of a comet consists of an agglomeration of meteors, the coma, of dust and vapor: and the tail, which is acquired only when near the sun, is the product of radiant and electric energies (acting on microscopic particles)in excess of the force of gravity, thus giving a direction always from the sun. The tail appears only when the comet comes near enough to the sun to be subject to its radiant and electric forces, and disappears when it passes beyond those influences. The periods of comets—the come tar y year—varies from a few months in some cases to thousands of years in others. Their courses reach often far beyond the orbit of Neptune, but no one knows how far some of them go. The lustre of a comet is enhanced if its advent occurs during a maximum sunspot period, therefore, also, during a period of maximum auroal display. The latest appearance of Halley's comet occurred when there was little sunspot activity, and the appearance was disappointing to some. Perhaps it might have been more stupendous had the sun been more active at the time. It is probable that comets and meteors keep always the same face sunward. Meteors are uncharted masses of adventitous matter floating in space around the sun. Coming within the earth's influence, they are drawn into its atmosphere, where the friction may melt them and turn them into vapor, or failing complete vaporization on account of their size, they may fall to the greound or into the sea, but in a few cases they pass through a part of the earth's atmosphere and out again into space. In the case of the meteors of February 9th, 1913, when several groups of large meteors passed over the western hemisphere and the mid-Atlantic ocean, it is not known certainly whether they reached the earth's surface and were lost in the sea, or passed out of the atmosphere and went on their way. The latter is perhaps the more probable theory. They were very large and were observed for some thousands of miles before they disappeared. Their height has been variously estimated at from 25 to 45 miles. They made a distinct sound which took some time to reach the ear because of their distance away. This sound was in most cases not heard till after the meteors that produced them were out of sight. The comparatively slow procedure of these objects across tlie sky was remarkable, and the whole p'cture so ably dealt with by Prof. Chant and others in the Journal of May-June, 1913, was one of the most startling and remarkable seen by the eyes of the present generation.s Many specimen meteorites are on exhibition at various centres. They are composed chiefly of stone and iron
This article was originally published with the title "Companions of the Sun—II"