# The Music of the Spheres/Chapter 15

CHAPTER XV
MERCURY, URANUS AND NEPTUNE
The Tiny Planet of Mercury, the Messenger of the Gods
Diameter—3030 miles
Mercury, the smallest and fleetest and hottest of the planets, shines as a star of the first magnitude. It lies closer to the sun than any other planet, which increases the difficulty of studying it. Most of the time it is either hidden behind the sun or is passing between us and the sun, and the only time when it is observable is when it is to the east or the west of the sun. Indeed it is so often hidden or lost in the brightness of the sun that it is rarely seen except by a professional astronomer.
Like Venus, Mercury is seen first on one side of the sun and then on the other. In the early spring it appears in the west almost invisible in the twilight; in the early autumn, in the east as a morning star just preceding or mingled in the rays of the dawn. It is always seen very close to the eastern or western horizon, never more than two hours before the sun in the morning nor more than two hours after it in the evening.
Because of the great inclination of the orbit of Mercury, it is seen in a transit across the face of the sun not more than thirteen times in a hundred years. This transit may only be seen in a telescope. If it so happens that it travels across the center of the sun, the journey consumes about eight hours, although the little black dot is skimming across the big, bright disk at the rate of 100,000 miles an hour. The next five transits will occur on ​November 8th, 1927; May 10th, 1937; November 12th, 1940; May 13th, 1953, and November 6th, 1960.
The eccentricity of the orbit of Mercury is so pronounced that its greatest and least distance from the sun varies nearly 15,000,000 miles. This causes considerable variation in the speed of this planet, for as the sun does not lie in the center of the orbit but at one focus, it is not compelled to go as fast on the far side as on the side nearest to this tremendous mass. Being so close to the great attracting force of the sun, it is however, forced to move faster than any other planet in the solar system in order that the right balance of speed may be obtained to counteract the gravitational pull which would otherwise draw him instantly to the burning surface. Mercury's average rate of speed around its orbit is 35 miles a second. Neptune, seventy-five times as far off, feels so much less this relentless pull that it can roll leisurely along at the comfortable rate of 3.4 miles a second with no fear of being drawn to destruction.
Mercury completes his orbit in 88 days and this is, of course, the length of his year. During this journey he always turns the same face to the sun. The heat on this side must therefore be terrible and the surface unmercifully scorched and possibly cracked. Moreaux, a French astronomer, thinks that it may even be so hot that it has oceans of lead and molten tin. A few features are discernible, and although faint, these features are fixed. The general impression gained is that the tiny planet is barren, rough and mountainous, bleak, seared and desolate, with one side sweltering in terrific heat and the other numbed with dark and cold. Since there is no appreciable atmosphere on Mercury, there must be no wind—no warm currents of air to flow from the hot side to the cold side, nor from the cold side to the hot side,—thus making what is already drear seem motionless and dead.
Yet there is often some alleviating quality to make the drear ​seem less drear. For instance, a slight exception may be taken to the statement that the day side of Mercury is always day and the night side always night. As an effect of libration, an oscillatory movement of the planet on its axis, there is a strip of ground on either side, where the dark and light hemispheres meet, upon which the sun rises and shines for 44 days and then sets, leaving it in 44 days of darkness. This strip of ground is 23½ angular degrees in breadth and enjoys a true day, although its "day" is as long as its year, and is equal to 88 of our earth-days.
The Strange Planet of Uranus, the Ancient God of the Heavens
Diameter—32,000 miles
Mercury, Venus, Mars and Jupiter have been known since antiquity but Uranus was the first planet to be discovered with the aid of a telescope. This planet was discovered in 1781 by William Herschel while mapping stars, and the very fact of its existence astounded the world. Because Galileo had named the satellites of Jupiter the Medician Stars after his patron, Herschel wished to name his newly discovered planet Georgium Sidus, in honor of George the Third. But foreign astronomers would not agree to this and until a name was decided upon, called the planet Herschel. Later, the planet was called Uranus after the most ancient of all the deities, and its sign was the sign of the world hung on the initial of Herschel. ♅ In appreciation of the fact that he had discovered a planet, Herschel was made private astronomer to his king and later knighted.
Uranus is the smallest of the major planets and ranks next to the earth in size, which is the largest of the minor planets, yet there is a great difference in the size of these two planets, for the ​diameter of the earth is only 7927 miles, while that of Uranus is 32,000 miles. There is also as great a difference in the nature of these two worlds.
Uranus travels through space in an orbit at an average distance of 1,771,000,000 miles from the sun, encompassing the orbits of Saturn, Jupiter, the Planetoids, Mars, Earth, Venus and Mercury; an orbit so large that it takes the planet 84 years to complete its journey around the sun. It has only been a year and a half, according to time figured on Uranus, since Herschel first introduced this planet to earth-dwellers.
Although the year of Uranus is 84 of our years long, which causes long and remarkable seasons, its day is very short, for the planet turns so rapidly on its axis that it sees both day and night in 10 hours and 50 minutes. Even the few hours of daylight it enjoys are not very bright ones, or warm ones either, for the planet is so far from the sun (which appears as an intense point of light), that it receives only $^1$⁄$_{360}$th as much light and heat as we do on earth.
The axis of Uranus is tipped 98 degrees from the perpendicular which causes not only extreme but peculiar seasonal changes. Since the axis of the planet is always pointing in the same direction and at one place in its 84-year journey points almost directly at the sun, each pole in turn is bathed in 42 years of dim daylight and then, when on the other side of the orbit, sleeps through a night that is just as long. Bürgel remarks that "an inhabitant born at the beginning of winter and dying at the age of forty, would never see daylight, or the sun, but live in everlasting darkness like the pit-ponies in coal mines. The contrary would be the case with the summer-born, who would know of night and the stars only from hearsay." Quite different from what life might enjoy on Jupiter, for Jupiter's axis is inclined only 3 degrees from the perpendicular and its year would be almost a perpetual spring.
​Careful observations seem to indicate that Uranus is a gaseous body, although cooler and more solid than Saturn and Jupiter. This planet is immersed in an exceedingly dense atmosphere quite different in constitution from the light, diaphanous covering of air which encloses the ball of the earth. This is indicated by the broad absorption band in its spectrum.
Uranus is attended by four moons but these are too far away for us to observe in any detail. Herschel discovered two of these soon after the planet was discovered, and they were given the names of Titania and Oberon. In 1851, Lassel of Liverpool discovered two more which were called Ariel and Umbriel. Two of these moons are seen with great difficulty even with the aid of the most powerful telescopes. The orbits of these moons are tipped nearly perpendicular to the plane of the orbits of the earth and Uranus, and their movements are retrograde as regards most of the known movements of the solar system.
This strange planet of the most ancient God of the Heavens is now visible during the spring and summer months as a faint, greenish star of the 6th magnitude, but it is rather difficult to locate unless the observer is an experienced astronomer.
The Boundary Planet of Neptune, the God of the Sea
Diameter—35,000 miles
After the discovery of Uranus in 1781, its pathway among the stars of the sky was carefully noted and geometers were not long in fitting it with an orbit. In a few years, however, it was noted that the planet was out of its computed orbit by a distance as great as the moon's distance from the earth. The deviations attracted general attention and popular opinion feared that the new planet, being so far from the center of the solar system, was ​breaking away from the sun's control. But a young mathematician, J. C. Adams, and a few months later an older and experienced mathematical astronomer, Leverrier, conceived a more logical solution of the mystery, and decided that they would search beyond Uranus and see if there was not a planet which was attracting Uranus and causing irregularities in the great world's motion. This was a tremendous task, for not only was it necessary to calculate the orbit of the hypothetical planet, but also the weight and speed that such a planet would have in order to pull Uranus in exactly the way that it was being perturbed. After much hard work the problem was satisfactorily solved by each man independently.
Challis at Oxford, following the computations of Adams, first commenced to search in the place where these indicated that the planet might be found, and on August 4th, 1846, actually saw and mapped the star but did not recognize its planetary character. On the 23rd of September, 1846, Galle of Berlin, searching at the place indicated by Leverrier, found the new world at almost the exact place indicated by the computations! This should satisfy the most skeptical as to the validity of the great Newtonian law of gravitation and the accuracy of the mathematical deductions therefrom. To prove the existence of a planet and to determine its position before it was ever seen, is considered by scientists to be among the most amazing intellectual achievements ever recorded in history.
Neptune requires 165 years to complete a revolution around the sun. The boundary line of the solar system, which is the planet's orbit, is a tremendously long pathway on which to travel, for it lies at a distance of 2,775,000,000 miles from the sun.
The length of a day on Neptune is not known as it lies too far away to permit an observer to distinguish any permanent surface features even with the largest telescopes.
​It has been estimated that as Neptune is so far away from the sun, it receives only $^1$⁄$_{900}$th as much light and heat as our earth.
The sun, as viewed from Neptune, would look very small, not much larger than Venus does to us when she is nearest the earth, although he gives to Neptune 250,000 times more light than Venus gives to us at her best.
Neptune possesses only one known satellite. This satellite has the peculiarity of whirling much as if it had been tipped over through an angle of 150 degrees, which causes it to move in a direction opposite to that in which the planets travel around the sun.