Saturn

Saturn  was recognized as a planet by the ancients, and was the outside member of the solar system as known by them. His diameters at the equator and poles differ considerably, the protuberance at the equator giving him there a diameter of 74,000 miles, while at the poles it is only 68,000. In size Saturn is the largest of the planets except Jupiter, being in fact seven hundred times larger than our earth, but his density is so small that he would be able to float on water far more easily than an iceberg. From this it follows that he cannot consist of solid or liquid matter, and in fact we can only view a mass of clouds intensely heated within, the whole being probably a planet in the early stage of development—younger even than Jupiter.

The most remarkable characteristic of Saturn, which makes him an object of such interest in the sky, is his possession of a luminous ring. The ring is only luminous on account of its reflection of the sun's light; hence is invisible to us when, for instance, we are endeavoring to look at the ring from below while the sun is shining above. It also sometimes happens that the plane of the rings passes through the sun or through the center of the earth, in which case only the thin edge of the rings can be seen. The ring is divided into two parts, the inner being the wider, while another faint division appears to divide the outer part into two smaller rings. In 1850 another ring was discovered; this is quite different from the outer rings, being dark, and generally known as the dusky ring of Saturn. The outer ones, though far from solid, can receive a shadow of Saturn, and themselves cast one on his disc. The rings are not continuous masses of matter, but consist of countless myriads of tiny satellites, so close together that to the observer they appear as one body. The planet has eight satellites which seldom pass behind or in front of the planet's disc, and therefore are not objects of great interest.

Was Saturn's Ring Known to the Ancients?

In Maurice's Indian Antiquities  is an engraving of Sani, the Saturn of the Hindoos, taken from an image in a very ancient pagoda, which represents the deity encompassed by a ring  formed of two serpents. Hence it is inferred that the ancients were acquainted with the existence of the ring of Saturn.

Arago mentions the remarkable fact of the ring and fourth satellite of Saturn having been seen by Sir W. Herschel with his smaller telescope by the naked eye, without any eye-piece.

The first or innermost of Saturn's satellites is nearer to the central body than any other of the secondary planets. Its distance from the centre of Saturn is 80,088 miles; from the surface of the planet 47,480 miles; and from the outmost edge of the ring only 4916 miles. The traveller may form to himself an estimate of the smallness of this amount by remembering the statement of the well-known navigator, Captain Beechey, that he had in three years passed over 72,800 miles.

According to very recent observations, Saturn's ring is divided into three  separate rings, which, from the calculations of Mr. Bond, an American astronomer, must be fluid. He is of opinion that the number of rings is continually changing, and that their maximum number, in the normal condition of the mass, does not exceed twenty. Mr. Bond likewise maintains that the power which sustains the centre of gravity of the ring  is not in the planet itself, but in its satellites; and the satellites, though constantly disturbing the ring, actually sustain it in the very act of perturbation. M. Otto Struve and Mr. Bond have lately studied with the great Munich telescope, at the observatory of Pulkowa, the third  ring of Saturn, which Mr. Lassell and Mr. Bond discovered to be fluid. They saw distinctly the dark interval between this fluid ring and the two old ones, and even measured its dimensions; and they perceived at its inner margin an edge feebly illuminated, which they thought might be the commencement of a fourth ring. These astronomers are of opinion, that the fluid ring is not of very recent formation, and that it is not subject to rapid change; and they have come to the extraordinary conclusion, that the inner border of the ring has, since the time of Huygens, been gradually approaching to the body of Saturn, and that we may expect, sooner or later, perhaps in some dozen of years, to see the rings united with the body of the planet. But this theory is by other observers pronounced untenable.

FIG. 19.

Far beyond Jupiter rolls another stupendous orb called Saturn, not so large as Jupiter, but still immense, being 847 times the bulk of the earth. It is placed at the distance of 906 millions of miles from the sun. An idea of this may be formed from the fact that light, which travels at the rate of nearly 200,000 miles a second or 12,000,000 a minute, takes about an hour and a quarter to pass from the sun to Saturn. It performs its journey round the sun only in 29½ years, which are therefore but as one year, yet all this time it is moving at the rate of nearly 22,000 miles an hour, so immense is the orbit it has to traverse, but it revolves on its axis in about 10½ hours, so that the nights and days are extremely short while the years are prodigiously long. There is every reason to believe that it has changes of seasons and variation of climate similar to those in our world, but, being so far from the sun, they must be altogether more severe than ours. The most extraordinary part of this great globe is its possession of three (perhaps more) great flattened rings, which surround it, one within the other; these rings are of immense size and width, but very thin, the great breadth through all from the inner to the outer edges being about 30,000 miles, while their thickness cannot exceed 250. These rings are placed at a right angle to the planet's axis of rotation and revolve with it, so that when the planet is at the equinox, the edge of these rings is turned towards the sun, they can then be seen only by the most powerful telescopes, forming a faint streak on each side of the orb of the planet (fig. 19), but as they become inclined they appear as a very long ellipse, the ends of which project in loop-like forms on either side, giving rise to the notion of the planet having two handles (fig. 20). This ellipse becomes broader and broader as the plane of the rings forms a greater angle with the line of vision. For a short time before and after the equinoxes of Saturn, the rings become invisible, owing to the earth and sun being on opposite sides of them, as may be seen in fig. 21, so that the darkened side is turned towards the earth and the edge, which is the only part illuminated, is towards the sun.

FIG. 20.
FIG. 21.




The inner ring of Saturn is supposed to be composed of watery vapour, as it is somewhat transparent, but the outer ones are solid, which is shown by the shadow they cast upon the planet, and the shadow it casts upon them in different positions (figs. 22 and 23). Besides these rings Saturn has eight satellites or moons, which revolve in a plane nearly parallel to that of the rings and exterior to them. It has been calculated that Saturn weighs only 100 times more than the earth, although it is somewhere about 900 times larger, from which it is concluded that the substance of which Saturn is made must be about one-ninth the density of this earth, half the density of water, or about the same as cork. Saturn is very much flattened at the poles, so much so that the equatorial diameter is a tenth more than the axial diameter, which difference is distinctly visible through good glasses.