Among the four planets that we commonly see, the easiest, perhaps, to keep track of is Saturn. Its peculiar aspect is very distinctly marked. It appears as a large, pale, yellow star shining with a soft, misty light that sometimes barely escapes being dull. It is always as bright as a first-magnitude star, but not always as bright as Sirius, and never as brilliant as Mars, Jupiter, or Venus when they are at their brightest. The general effect of it is as a large rather than a brilliant star.

The only time it loses these very marked characteristics is when it is drawing in toward the sun, and thus nearing conjunction. At such times we see it each evening lower in the rosy glow of the setting sun, and more and more obscured and changed in color by the surrounding atmosphere. Then it sometimes seems as red as Mercury, and sometimes even twinkles a little in a sort of farewell gaiety as it backs away from us into the rays of the dazzling sun and finally disappears for a time from the evening sky. Proximity to the sun and entanglement in the atmosphere of the horizon has this effect more or less on all the planets, as we know, but it always seems unexpected in Saturn, because it is so out of keeping with his ordinarily large, pale, placid face, which suggests softness and gentleness rather than vivacity.

But there is no mistaking the planet even under this aspect if we but stop to think where he is. And it is through knowing where he is that it is so easy to keep track of Saturn. For nearly two years and a half, on an average, he remains in the same constellation, passing slowly over about one degree a month, or a little more than twelve degrees in a year, occupying almost thirty years in making one circuit through the constellations of the zodiac. One has, therefore, ample time to get well acquainted with him before he has wandered far from the position in which one first found him.

For nearly six months each year Saturn shines as an evening star, and, returning each year as he does with such slight changes of position, he comes to have something of the stability of a fixed star. Having seen him one year, we can count on his returning the next only about thirteen days behind time, and but little farther from his original position than twice the distance between the pointers in the Big Dipper.

The one degree a month which he travels along the ecliptic is toward the east, except for a little more than two months before opposition, and the same length of time afterward, when he has the slight apparent retrograde motion due to our overtaking and passing him, which has been explained. With Saturn this motion is so slight—only four degrees—that it does not put him much out of position, and it is, in fact, not much noticed except by close observers. He has all the time been going steadily on toward the east (for the retrograde motion is only an apparent motion), and the annual change of twelve degrees in position is always in this direction.

My first acquaintance with Saturn was when he was traveling through Pisces and Aries, where there are no first-magnitude stars to mark the path of the wandering bodies in the heavens. It was then that I was most impressed with the fixity and reliability of his return. Every autumn then for five years we watched Antares passing toward the west, followed by the little “milk dipper” in Sagittarius; and then Fomalhaut, crossing the sky in the same direction, though below the constellations of the zodiac; and then turned our eyes toward the east, knowing that the next bright body to come peeping over the tops of the trees would be Saturn. And when the first frosts began to strip the leaves from the trees we found the compensation that nature always gives when she destroys one beauty: we could see earlier in the evening, through the bare branches, that lovely yellowish disc, with its suggestion of aloofness and grandeur that is peculiar to it. For the face of Saturn, while never what we would call cold, has little in it of that bright, warm, friendly aspect which is at times so characteristic of Venus, Mars, and Jupiter.

AROUND ONE CIRCUIT OF THE SKIES WITH SATURN

Saturn is now (the autumn of 1912) in the first part of his path through Taurus, and he will be in that constellation during all of 1913 and the greater part of 1914.

From 1912 to 1920 he will be a beautiful object in the winter sky, threading his way slowly through that splendid galaxy of stars that blazes across the glittering sky peculiar to the cold winter nights. He will pass between the Pleiades and Aldebaran, and will be in opposition in that region on November 23, 1912. Farther east in the constellation he will be in opposition in the first week of December, 1913. Almost on the border line between Taurus and Gemini he will be in opposition during the third week in December, 1914; and, as this is very near the perihelion point in Saturn’s orbit, the planet will then be at his brightest.

In 1915 he will not be in opposition at all; but sometime within the first two or three days of 1916 he will reach that position, and will then be well on in his journey across Gemini. For these four years—from 1912 to 1916—he will be visible during the entire night, at the times of his opposition, and in his best condition. The rings that surround him will then be placed so that we will get a broad expanse of light from them, as well as from the planet itself, which greatly increases its brightness.

Saturn will then continue to move across Gemini, passing in the early part of 1917 under Castor and Pollux, and very near to Neptune—a meeting which, unfortunately, cannot be seen with the naked eye. During this year (1917) he will begin his journey through the smallest of all the constellations of the zodiac, Cancer, passing near the lovely cluster of stars we call the Bee-hive, and will reach Leo early in 1919, where he will remain until about the end of 1921. While in this region he will be visible during the winter and all of the spring and the early summer. All three of these constellations—Gemini, Cancer, and Leo—while seen in the winter, are particularly lovely in the spring. Gemini, in the beautiful evenings of May, hangs with its two splendid stars in the northwest above the setting sun; and with the soft face of Saturn near them, these stars will be more than ever charming in the two seasons that the planet remains with them.

In 1917 Saturn will be in opposition in the region of Gemini, about the middle of January. In 1918 opposition will occur about the last of January, and Saturn will then be in Cancer. The next year he will be in opposition sometime during the second week in February, and will then be situated between the Bee-hive, in Cancer, and the brilliant first-magnitude star Regulus, in Leo. The next two oppositions will be in Leo, about thirteen days later each year. Saturn will then pass during the first half of 1922 into Virgo, which is the largest of all the constellations, and he will remain there until three oppositions have taken place, about thirteen days later each year.

About a year after passing Spica, the white, sparkling, first-magnitude star in Virgo, Saturn will enter Libra, crossing that constellation near the lower part of the square in it. From there he will go through Scorpio and Sagittarius, passing above Antares and the “milk dipper,” and in about 1932 will have reached that comparatively starless region which includes a part of Sagittarius and all of Capricornus, Aquarius, Pisces, and Aries. For the next nine and a half years he will give distinction to this part of the heavens, and thus complete his circuit of twenty-nine and a half years, and, with never resting, never changing movement, will start on a new round, with a new generation of eyes following his fair face along the great circle of the ecliptic.

Saturn is brightest when he is in Taurus, not far from Gemini, as he will be in 1914, and again when he is in Scorpio, as he will be between fourteen and fifteen years later. The recurring times at which we can get an evening view of him at his greatest brightness thus alternate between midwinter and midsummer. He is least bright when he is in the last half of Leo and when he is in that part of Aquarius above Fomalhaut. Between these positions he gradually waxes and wanes in brightness, changes that are largely due to the position of his rings.

Saturn is almost twice as far from the sun as Jupiter, and between nine and ten times farther than we are. His mean distance from the sun is eight hundred and eighty-seven million miles; but his distance varies nearly one hundred million miles between perihelion and aphelion. His orbit is only a trifle more eccentric than that of Jupiter, but the variation in miles is so much greater because the orbit is so much larger.

His average distance from the earth at opposition is seven hundred and ninety-four million miles, but at the most favorable opposition it may be fifty million miles nearer than that. At conjunction his average distance is nine hundred and eighty million miles; but his greatest possible distance at such times may be as much as one billion miles. When he is in this situation it takes light a little more than an hour and a half to pass from him to us. At his nearest we receive light from him in about an hour and six minutes. At his average distance from the sun, light requires about an hour and twenty minutes to go from one to the other.

While Saturn is next to Jupiter in size among the planets, he is not as large as Jupiter by two-thirds, but his mass is almost three times greater than that of all the other planets put together except Jupiter. It is ninety-five times greater than that of the earth. In diameter Saturn is 72,772 miles; but it is more flattened at the poles than any other planet, and in consequence there is a difference of nearly seven thousand miles between its polar and its equatorial diameters.

The density of Saturn is less than that of any other planet, and it is ten times less than that of the earth. No other planet is less dense than water; but Saturn would float in water, and is not more dense than cork. On account of its mass its gravity is greater than that of the earth by about one-tenth. This is not enough to make a very interesting difference in the weight of objects on Saturn and on the earth. The average person weighing one hundred and fifty pounds here would weigh only one hundred and sixty-five pounds on Saturn. The numerous penny-in-the-slot weighing-machines vary almost that much. Saturn has eighty-three times more surface than the earth, and more than seven hundred and fifty times the earth’s volume.

SURFACE ASPECTS AND CONSTITUTION

It is not at all certain that Saturn, more than Jupiter, has any solid surface. Indeed, it is almost certain that it has not. It is surrounded by an atmosphere of great density, and we do not at any time see the surface of the planet. It is believed probable that it is at least largely in a liquid state, if not to a great extent even gaseous.

The planet is certainly not in any way dependent on the sun for the extraordinary heat that everything indicates it to have, and its surface is brighter than it is believed it could be if shining only by the reflected light of the sun. This does not mean that Saturn is self-luminous; but it is nearly certain that it is extremely hot and glowing, and its brightness may be in part due to its own internal fires and the extremely luminous and dense atmosphere that surrounds it. It receives one hundred times less heat and light from the sun than we do. If it depended entirely upon the sun for its heat, the temperature would be nearly three hundred degrees below zero, Fahrenheit. It is probably not only very hot itself, but its heavy atmospheric envelope perhaps allows comparatively little heat to escape.

Its surface is belted and spotted somewhat after the manner of Jupiter’s, but, being so much farther from us than Jupiter, it does not disclose its surface features with the same distinctness. Apparently it is much less turbulent than Jupiter; but even this we are not quite certain of, and it may seem more placid because we do not so well see its agitations.

Like all the outer planets, it differs in its constitution from the earth and the other inner planets. Its atmosphere contains compounds with which we are not familiar, and the body of the planet itself is rarer and lighter, and less condensed, and in a much earlier stage of evolution than the earth and the small planets so comparatively near us.

DAY AND NIGHT

The length of Saturn’s day, or its period of rotation on its axis, is about ten hours and a quarter. Like Jupiter, it has slightly different rates of rotation in different latitudes, thus showing its lack of solidity. The rate of rotation has been determined, as in the case of Jupiter, by observation of the spots on its surface, which, while they are not exactly permanent, yet remain apparently in the same positions for months and even years at a time, and are thus sufficiently stable to measure a rotation of so short a time as ten hours.

Whirling over at this rate would cause the sun to appear to skim across the sky very swiftly as viewed from Saturn. In size, it would not seem more than three times as large as Venus at her brightest seems to us, and every minute it would cover a distance about equal to the diameter of the full moon as we see it. In an hour it would seem to move more than six times as far as the distance between the “pointers.” At the time of Saturn’s equinox the little five-hour day, followed by the equally short night, must present a lively aspect with the sun racing thus swiftly across the sky in daylight and the stars sweeping as swiftly over at night. If things remain as they now are, it will be a splendid panorama for the people there when, in the far-distant future, Saturn may have cooled and solidified sufficiently to maintain life somewhat as we know it. The earth, though, and Venus and Mars would be from Saturn only telescopic objects to eyes like ours, and Jupiter no brighter than he is to us. Thus does our brother Saturn pay the price of his remoteness from the rest of the solar family.

THE RINGS AND MOONS OF SATURN

But the circling stars and the swift-moving sun are the least part of the splendid spectacle that might be seen from Saturn. He is surrounded with no less than ten moons of more or less imposing size, and in addition has three rings circling around with him, composed of myriads of small satellites, together forming a band the outer diameter of which is something more than twenty-one times broader than the diameter of the earth. These are the famous rings of Saturn, the only objects of their kind in the solar system, intensely interesting to scientific observers, wonderful to the curious, and splendidly beautiful to everybody. It is this profusion of rings and moons that entitles Saturn to be called, as he often has been, the most spectacular of all the planets.

The outer ring is nearly ten thousand miles broad, and is separated from the next one by a space of about seventeen hundred miles. The second ring is nearly eighteen thousand miles across. It is very bright on the outer edge, but gradually grows less so, until, with a not very perceptible division, it fades into the inner ring, which is but slightly luminous, and is called the crape ring. This is about nine thousand miles broad and nearly ten thousand miles from Saturn. This gradual fading of the rings to a dusky hue toward the center, and then the blackness of the space between them and the planet, gives them from certain points of view a nest-like appearance; and my first impression of Saturn, when I saw him through the telescope, was that he was nestling in a concave body of light—an appearance that is intensified by his extreme flatness at the poles.

Notwithstanding the imposing breadth of these rings, they are less than a hundred miles in thickness. They are, in fact, nothing more than an untold number of tiny satellites revolving about Saturn in the same plane and close enough together to appear, at the distance they are from us, as if they were one body. Just how close they are together, and how they appear when near by, we do not yet know. It was first shown by mechanical laws that they must be composed of separate bodies; the spectroscope shows that they are; and it has recently been thought that they have even been seen to be so through a telescope.

Being all in the same plane, they form a flat, broad, thin ring, so thin that when the edge of the ring is turned toward us we cannot see them at all. We never see them at their full breadth. If we did, Saturn would be much brighter at times than he ever is. The plane in which they revolve is the plane of Saturn’s equator; and the axis of Saturn, with the rings, has a tilt of twenty-seven degrees in his orbit. The result of this is that at the time of Saturn’s equinoxes the edge of the rings is turned toward us, and they practically disappear. Half-way between the equinoxes they are open again as far as they ever are to our view. This is why Saturn alternates in brightness. The times of his equinoxes occur every fourteen and eight-tenths years, and he is then alternately in Leo and Aquarius and is least bright. The times at which the rings are most open occur at intervals of the same length, and he is then alternately in Scorpio and Taurus and at his brightest.

It is believed that Saturn’s rings were never a part of the planet, but are mere particles of cosmic materials which happened to be left over, and which he has gathered up by his force of gravity and compelled to revolve about him.

Saturn, more fortunate than Jupiter, has escaped the unimaginative naming of his moons by number, though one would think that, having such a numerous offspring, a shortage in names would be more likely to occur in his than in any other planet family. They all have names more or less connected with the great god whose name the planet bears, and are, in order of their distance from Saturn: Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Japetus, Phoebe, and Themis. The largest and brightest of them all is Titan. It is larger than our moon, which is one of the large moons in the solar system, or than Mercury, and is not much smaller than Mars. It is more than three-quarters as large as all the other moons of Saturn put together. Naturally, it was the first to be discovered, and was under observation as long ago as 1655. Rhea and Japetus are next in size, and were discovered in 1671–72; Dione and Tethys were both discovered in 1684, and Enceladus and Mimas in 1789.

Until 1848 seven moons were all that were known to belong to Saturn. In that year little Hyperion, whose diameter, it is thought, can hardly exceed two hundred miles, came into our view. A little more than fifty years later (in 1898) Phoebe made her bright mark on a photographic plate at Harvard, and was caught. By tracing her from one plate to another her orbit was computed, her probable size determined, and practically all that is known about her was found out before she was seen, which was not until 1904. She is not much larger than a good-sized mountain, but is a unique and interesting little satellite that, far outside of the paths of any of the other moons, circles in an eccentric orbit around Saturn in an opposite direction from the rest of the satellites, and thus gives rise to many interesting astronomical speculations. Themis, also a tiny body, was discovered in the same way in 1906, and is thought to be the smallest body in the solar system. Titan is the only one of this group of satellites whose true disc we can see even with a telescope. Only one other (Rhea) can be seen in transit across the planet. The others are not much more than bright points of light, while Phoebe and Themis are almost at the limit of visibility.

On account of their great distance from the sun Saturn’s moons are, of course, not very bright, and all of them put together do not give one-tenth as much light to Saturn as we receive from our moon. But, such as they are, they may some day be very useful to Saturn as a means of illumination. Receiving as he does a hundred times less light from the sun than we do, he may be some day much in need of the light reflected from all his rings and moons.

SEASONS

The seasons on Saturn are somewhat like ours in the succession of spring, summer, autumn, and winter; but the inclination of its axis to its orbit being twenty-seven degrees instead of twenty-three and a half, as ours is, each season is much more accentuated than ours. The sun climbs higher during the northern summer, and sinks correspondingly lower during the winter. But in length Saturn’s seasons are very different from ours. Like his year, they are about twenty-nine and one-half times as long as ours. Each one is more than seven years long. Even the agreeable seasons might grow monotonous to one in that time; but to be spinning through the rapidly alternating days and nights of Saturn during seven long years of winter is a situation that one does not care to contemplate. It is with world personalities as with human personalities: however much we may admire their superior grandeur, when we consider details we would not change places with them.

The symbol of Saturn is an ancient scythe (?), which gets its appropriateness from the fact that the deity of that name was the special protector of agriculture.