Jupiter's moons

“ The movement of our moon, however embarrassing a problem it may present to mathematicians, is, nevertheless, simplicity itself in comparison with the movement which has to be performed by one of Jupiter's moons. In the case of each of these little bodies there is not only a force exerted by the sun with the effect of disturbing the satellite's motion, but each one of the four globes attracts each one of the others, and is in turn attracted by it. ”

“ Jupiter's moons will be like head and stern lines in enabling you to choose the part of the surface on which you wish to land. With apergy it is as essential to have some heavy body on which to work, within range, as to have water about a ship's propellers. Whether, when apergy is developed, gravitation is temporarily annulled, or reversed like the late attraction of a magnet when the current is changed, or whether it is merely overpowered, in which case your motion will be the resultant of the two, is an unsettled and not very important point ”

“ He too sometimes so diminished in lustre, as not to be easily discovered. But a new and beautiful system will arise. The four moons of Jupiter will become very conspicuous; some of them perhaps appearing larger, others smaller than our moon; and all of them performing their revolutions with incredible swiftness, and the most beautiful regularity:—varying their phases fromfrom full to new and from new to full, and frequently eclipsing the sun and each other, at least to the equatorial parts of Jupiter; and almost in every revolution suffering eclipses themselves by falling into Jupiter’s shadow ”

“ To those not specially conversant with the principles of mechanics, it may seem difficult to realise the degree of accuracy of which such a method is capable. Yet there can be no doubt that his moons inform us of the mass of Jupiter, and do not leave a margin of inaccuracy so great as one hundredth part of the total amount. If other confirmation be needed, then it is forthcoming in abundance. A minor planet occasionally draws near the orbit of Jupiter and experiences his attraction; the planet is forced to swerve from its path, and the amount of the deviation can be measured. ”

“ Whether Jupiter appears with dark stripes upon its surface, or is uniformly illuminated, pertains as little to the inquiries of the astronomer; and its four moons are interesting to him only for the motions they have. To learn so perfectly the motions of the celestial bodies that for any specified time an accurate computation of these can be given—that was, and is, the problem which astronomy has to solve.'
There is a curious irony of progress which seems to delight in falsifying the predictions of even master minds as to the limits beyond which it cannot advance. ”

“ The same unquestionably holds true for other stellar bodies of equal or smaller size, such as all the minor planets and for the great majority of the satellites to the major ones. Only the very largest of Jupiter’s moons, and possibly Neptune’s lonely companion, whose size is not known with certainty, might possibly surpass our Moon in ability to retain gases. ”

“ Although Jupiter appears to move slowly, it really travels at the incomprehensible rate of five hundred miles a minute.
The most interesting feature about Jupiter for the amateur astronomer consists in observing four of its moons, which are visible with a small telescope. They appear like mere dots of light, and their transit of or occultation with the planet (that is, their disappearance before or behind its disk) can be watched, and is a never failing source of pleasure. A large telescope alone reveals Jupiter's four other moons. ”

“ They are continually causing solar [Pg 182] eclipses and themselves undergoing eclipse in Jupiter's shadow, and their swiftly changing aspects and groupings would be watched by an astronomer on Jupiter with undying interest.
But far more wonderful would be the spectacle presented by Jupiter to inhabitants dwelling on his moons. From the nearer moon, in particular, which is situated less than 220,000 miles from Jupiter's surface, the great planet would be an overwhelming phenomenon in the sky. ”

“ For, Jupiter turning about the Sun, does nevertheless turn about his Axis; and although he be much bigger than the Earth, he does nevertheless turn much more swiftly than it, since he makes more than two Turns, and a third part, for its one; and carries with him 4. Moons, as the Earth does one.
This Observation ought to excite all Curious persons to endeavour the perfecting of Optick Glasses, to the end that it may be discovered, whether the other Planets, as Mars, Venus and Mercury, about whom no Moon hath as yet been discovered, do yet turn about their Axes, and in how much time they do so ”

“ Jupiter is enlightened by four moons, or satellites, each of them larger than that with which we are supplied, and which revolve at different distances from that planet. In the solar system the moons, or satellites, revolve round their respective primary planets as 240 centres, in the same manner as the primary planets revolve round the sun. By means of Jupiter’s satellites, a method has been obtained for demonstrating that the motion of light is progressive, and not instantaneous, as was formerly supposed; which discovery is important to the interests of science. ”

“ It shines merely as the earth itself shines, or as the moon shines, or the planet Mars, or Venus, or Saturn, by the sunbeams which fall upon it. As to the light which illumines the satellites of Jupiter, it also can only come from the sun. We cannot, indeed, say that the light-radiating power of a certain area on Jupiter is the same as that from an equal area on one of his moons. There are certainly intrinsic differences between the material constitution of the great planet and of his satellites which prevent us from affirming that they are at all times equally capable of reflecting light. ”

“ Sometimes, I suppose, Jupiter has the benefit of four moons all shining at once?” asked Servadac.
Of the satellites, Lieutenant Procope went on to say that one is rather smaller than our own moon; that another moves round its primary at an interval about equal to the moon’s distance from ourselves ”

“ We see the little moons on account of their light, and light takes time to travel. Don't you remember, I told you sound travels a mile in five seconds. Light travels even [90] more quickly, for it only takes a little over a second in coming to us from the moon. It takes about eight minutes in coming to us from the sun; but Jupiter is about five times as far away from us as the sun, so that light takes about half an hour in coming to us from Jupiter. We do not see it as it is, but as it was more than half an hour ago, when its rays of light started out to Planet Earth. ”

“ The real motion of them all is from west to east, though sometimes they appear to move from east to west; and at other times seem not to move at all. And hence they are said to be direct, retrograde, and stationary. The Earth, Jupiter, and Saturn, are often eclipsed by the interposition of their respective moons, or satellites, between the sun and themselves ”

“ It is nearly as large as Jupiter, and has a huge ring of planetary matter revolving round it in addition to seven moons. Further and further we go, and the planets behind us are disappearing, and even the Sun is dwindling down to a mere speck; still we hurry on, and at last alight on another planet, Uranus, about sixty times larger than our Earth; we see moons in attendance, but they have scarcely any light to reflect; the Sun is only a star now; but we must hasten on deeper and deeper into space. ”

“ The satellites of the other planets, by their comparative proximity, must be much easier to study than our Moon. The Saturnians, the Uranians, the Jovians, cannot have had very serious difficulty in effecting some communication with their satellites. Jupiter's four moons, for instance, though on an average actually 2-1/2 times farther from their planet's centre than the Moon is from us, are comparatively four times nearer to him on account of his radius being eleven times greater than the Earth's. With Saturn's eight moons, the case is almost precisely similar. ”

“ The most recent observations tend to make us believe that the equatorial regions of Jupiter, like those of the sun, make more turns in a year than the polar ones; while the darkening toward the edge is another sunlike feature, though perhaps due to a distinct cause, and this is beautifully brought out when any one of the four moons which circle the planet passes between us and its face, an occurrence also represented in our figure. ”

“ We had talked it over for months, weighing the opinions of Earth's foremost astronomers. No "watcher of the night skies" could tell us very much about Jupiter. The year 1973 had seen the exploration of the moon, and in 1986 the crews of three atomotor-propelled space vessels had landed on Mars and Venus, only to make the disappointing discovery that neither planet had ever sustained life.
By 2002 three of the outer planets had come within the orbit of human exploration. There were Earth colonies on all of the Jovian moons now, with the exception of Ganymede. ”

“ It is curious to perceive how, not only in the case of our own moon, but in the cases of the moons of Jupiter, Saturn, and Uranus, and actually in those of all the planets considered as the moons of the sun, the Platonic epicycle really holds good. The earth turns on her heel, with the moon held out at arm's length, while she goes round the amphitheatre before the solar eye ”

“ They care nothing for scientifics which are of human erudition.'
[29] Similar reasoning applies to the moons of Jupiter, and it so chances that the result in their case comes out exactly the same as in the case of Saturn; all the Jovian moons, if full together, would reflect only the sixteenth part of the light which we receive from the full moon. ”

“ Our moon is by no means a minute body by comparison with the earth, and compared with Mars or Mercury she may be regarded as having very respectable dimensions. We may, indeed, look upon the moon as a fifth member of the inner family of planets—a member inferior to the rest, doubtless, but still not so far inferior to Mercury as Mercury is inferior to the earth. In the case of the outer planets, however, and especially in Jupiter's case, moons hold an utterly subordinate position. ”

“ Nearly two hundred and fifty years ago it was proved that light travelled at least 600,000 times faster than sound. Jupiter, as we saw, has moons, which circle round it. They pass behind the body of the planet, and reappear at the other side. ”

“ All the major planets have a single moon, or more, [Pg 160] revolving around them. For example, Jupiter has four moons; Uranus, six; Saturn, eight; Neptune, one. As to the minor planets, Mars has two moons; and, as far as is known, neither Mercury or Venus has a moon. Our earth has one moon, but, as we shall afterwards see, this is not to be regarded as a moon or satellite of the earth, but rather as a twin planet to the earth.
LaPlace's nebular hypothesis was proposed by LaPlace during the year 1796. ”

“ Jupiter is 1250 times larger than the earth, and has seven moons, and this planet with its moons revolves and illumines the sky to affect the spleen of Master Jack Sparrow and disturb the courtship of Mistress Jenny Wren. ”

“ I do not know that there is anything impossible in the supposition that the sun might, by an augmented volume and an augmented velocity of rotation, contain many times the moment of momentum that it has at this moment. It therefore follows that if it had happened that Jupiter constantly bent the same face to the sun, there would apparently be nothing impossible in the fact that Jupiter had been born of the sun, just as the moon was born of the earth. These same considerations should also lead us to observe with still more special attention the development of the earth-moon system. ”

“ Thus, by a strange arrangement of nature, our planetary system seemed destined to lose Saturn, its most mysterious ornament,—to see the planet accompanied by its ring and seven satellites, plunge gradually into unknown regions, whither the eye armed with the most powerful telescopes has never penetrated. Jupiter, on the other hand, the planet compared with which the earth is so insignificant, appeared to be moving in the opposite direction, so as to be ultimately absorbed in the incandescent matter of the sun. Finally, the moon seemed as if it would one day precipitate itself upon the earth. ”

“ When Several thousand miles above the pole, they diverted part of the power to attracting the nearest moon that was in the plane of Jupiter's equator, and by the time their upward motion had ceased were moving well in its direction. Their rapid motion aided the work of resisting gravity, since their car had in fact become a small moon, revolving, like those of Uranus or that of Neptune, in an orbit varying greatly from the plane of the ecliptic. ”

“ In fact, the slight obliquity of the lunar axis keeps the sun there at an almost equal altitude under every latitude. Above the equatorial regions the radiant orb almost invariably occupies the zenith, and hardly passes the limit of the horizon in the polar regions. Therefore, in each region, according to its position, there reigns perpetual spring, summer, autumn, or winter, as in the planet Jupiter, whose axis is also slightly inclined upon its orbit. ”

“ This fact at the time of its announcement was unique in the whole solar system. There was never a case known before in which a secondary planet accomplished a revolution in less time than the primary accomplished a rotation. And so far as this discovery in regard to Jupiter goes, the peculiar feature of the inner moon of Mars still remains unique. Even though the period of the satellite is only about twelve hours, it is still about two hours longer than the time which Jupiter requires to spin round his axis. We ought, however, here to notice that the rotation of Jupiter is exceptionally rapid. ”