Part 4

VENUS

This is one of the brightest and most beautiful “stars” in the sky, and has for long been the theme of poets. It is practically the same size as our earth, its diameter being approximately 7,500 miles. It travels round the Sun in 224 days, at a mean distance of 67,000,000 miles. It revolves on its own axis in about 23½ hours, so that its days are nearly the same as ours. It is thought that Venus has a fairly dense atmosphere, and also water-vapor, which proves the existence of water upon its surface. Dense layers of cloud exist in the upper regions of its atmosphere, making direct observations of its surface very difficult. For this reason, comparatively little is known as to the conditions on the surface of Venus. Every eighth year Venus passes through a period of great brilliance, being then so bright as to cast a shadow, like the Moon. Venus must have a higher temperature than our earth; its sky is always overcast; thunder and lightning must be never-ending. Some controversy has existed as to the habitability of Venus; but the consensus of opinion is that life would be practically impossible upon its surface.

THE EARTH

The earth on which we dwell was thought by the ancients to be the center of the entire Universe--the Sun, stars and the vast host of Heaven were thought to revolve around it. This was the so-called “geocentric” theory. It was later on displaced by the so-called “heliocentric” theory, when it was found that the Sun, and not the Earth, was the center of our system. It only remains to be said that our Earth is the third of the planets which revolve round the Sun--Mercury and Venus being nearer the Sun than we are, and the others still further removed in space. We are thus but one of a number of similar bodies moving through space, all revolving round the central Sun.

MARS

This now-famous planet is somewhat smaller than our earth, being about 5,000 miles in diameter. It travels round the Sun in 686 days, at a mean distance of 140,000,000 miles. The eccentricity of its orbit is considerable. Mars appears to us reddish in color, owing to the vast stretches of arid soil (desert) which exist upon its surface. Water exists, but it is relatively scarce; it is gradually drying-up, as it does in the case of all bodies of the kind--the water on our own earth is very gradually becoming less and less, as the centuries pass.

Mars has been drawn particularly to the public’s attention, of late years, by reason of the dispute (still raging) as to its habitability, and the character of its so-called “canals”--the more or less regular markings, like long, dark lines which have been seen to exist upon its surface. Its surface has accordingly been studied minutely for many years, but it may be said that no unanimity of opinion exists as to its being an inhabited planet. Says Kæmpffert, in his “Astronomy,” (pp. 183-84):

“The mapping of Mars is no recent matter, for even in 1659 a rough sketch of the surface of the planet was made by Huygens, in which the V-shaped markings at the equator, pointing to the north, can be identified as the Syrtis Major. This was followed by rough sketches from time to time down to 1840, when Maedler first began a systematic charting of the planet. His map was followed in 1864 by Kaiser’s, by Flammarion’s in 1876, and Greene’s in 1877. Drawings of various parts of the planet were made during these intervals, but were not combined into good charts.”

“Observations made by Prof. Lowell and his staff at the Observatory, at Flagstaff, Arizona, have had a study of this planet especially in view.... The surface of Mars as seen in the telescope, is composed of two white polar caps, which wane with the approach of summer; orange areas, which are supposed by Lowell to be deserts, and blue-green areas, which change their hue to orange during the Martian autumn and winter, and resume their verdant tint in spring. The planet is covered with a network of fine lines, first discovered by Schiaparelli, in 1877; and called by him ‘canals’--a designation by which they are still known. These canals connect the polar caps with the temperate and equatorial zones. According to Prof. Lowell, they may be regarded as planetary irrigation ditches, which serve the purpose of leading the melting water of the poles to those desert regions which would still blossom, if properly watered. The canals disappear with the approach of winter, and creep down from the poles towards the equator in summer--a phenomenon which long puzzled astronomers, until Pickering ingeniously suggested that we see, not the canals themselves (for they are much too narrow) but the vegetation which fringes their banks--which withers as the cold of winter descends, and which flourishes with the melting of the snows.”

It may be said that this theory of the canals on Mars is not universally accepted by astronomers, but is warmly disputed in some quarters. The markings are undoubted; but some astronomers are inclined to think they are due solely to vegetal growth, and are not the result of human hands. The controversy still continues. Meanwhile, two satellites of Mars were discovered in 1877.

JUPITER

Jupiter is the largest of all the planets, having a diameter of about 88,000 miles; it is only about 1,000 times smaller than the sun--that is, about 1,000 times larger than our earth. In volume, it is 1,300 times larger than our globe. Gravitation must be enormous on its surface. Its density is however relatively low--being only about one-quarter that of the earth. It is thought to be a world of water and more or less dense gas. It is constantly covered by a thick blanket of clouds and vapors, making direct observation very difficult--as we saw was the case with some other planets. Immense as this planet is in size, it revolves at a tremendous speed--approximately 10 hours. Owing to its immense bulk, it cools more slowly than a body such as our earth. Consequently it will take tens of millions of years for it to cool sufficiently to permit life to become manifest upon its surface. Yet it may at that time! In a sense, Jupiter may be said to be a planet of the future; when our earth is cold and dead, Jupiter may be teeming with animate existence.

Jupiter has 8 satellites, and a number of dark bands cross its surface from east to west. A certain dark spot upon its surface has caused great interest among astronomers, who are unable to determine its exact nature. This planet revolves round the Sun in rather more than 11¾ years, at a mean distance of 483,000,000 miles.

SATURN

Saturn revolves round the Sun in 29½ years, at a mean distance of 886,000,000 miles, in an orbit slightly eccentric. According to Barnard, its equatorial diameter is 76,470 miles, and its polar diameter 69,770, which figures imply a polar compression of 1/11. This planet is famous for the celebrated “ring” which surrounds it. As a matter-of-fact, when observed by means of high-powered telescopes, this famous “ring” is found to consist of a number of rings--three being clearly distinguishable. For long it was thought that these rings were vaporous; then that they were solid; but the present view is that they are composed of myriads of discrete particles of matter, so closely compacted together that to our remote eyes they appear as a solid mass. These rings are fairly broad, but relatively thin in diameter; they resemble a sort of huge disk. Perhaps 100 miles would be the thickness of these rings. Their diameter, however, is tens of thousands of miles in breadth. Owing to these rings, Saturn is one of the most beautiful of all the planets, when viewed through a high-powered telescope.

Saturn doubtless has certain features in common with Jupiter, as to its physical appearance. The general hue of the planet is yellowish-white; it probably has no atmosphere, or at most a very tenuous one. It is attended by ten satellites, the largest of which is known as Titan, thought to be about 2,700 miles in diameter.

URANUS

This is the next to the last planet in our solar system. It is a large planet, having a diameter of about 31,000 miles. Uranus revolves round the Sun in rather more than 84 years, at a mean distance of 1,781,000,000 miles. It is attended by four (or five) satellites. Belts and spots have been seen upon its surface, but relatively little is known concerning its physical conditions, owing to its great distance from us, and its relative smallness. This planet was discovered, as is well known, by Herschel, and was named after him, but its name was subsequently changed. (It is still mentioned as Herschel, in certain books upon Astrology.) It is probable that the temperature of Uranus is relatively low, owing to the small percentage of the sun’s rays which reach its surface. It has been calculated that its theoretical temperature is about 330° F.

NEPTUNE

The past century was remarkable for the discovery of this new planet: Neptune. How it was accomplished is a matter of great interest. In 1820, it was found that Uranus was not following its computed path. Adams, of Cambridge, and Leverrier, of Paris, each independently took up this question, and, assuming that this perturbation was due to the presence of a planet still more remote from the sun (which had been hinted at in 1830 by Bessel) they set to work to calculate its position in the heavens. They finished this at about the same time, arriving at practically the same conclusions. Adams’ results were first submitted to the Astronomer Royal, who set them aside without consideration until too late. Leverrier sent his conclusions to a German astronomer, Galle, who found the planet the first evening he looked for it, September 23, 1846.

Neptune is the furthest known planet of our solar system; it is a very large body, having a diameter of about 37,000 miles. It revolves round the sun in an immense orbit which it takes 164 years to complete. Its mean distance from the Sun is nearly 2,800,000,000 miles--a majestic sweep through the heavens! Relatively little is known as to the physical conditions of Neptune, owing to its immense distance, and its relatively small size. At least one satellite is known to exist. The temperature on Neptune must be extremely low, owing to its distance from the sun, whose rays would be exceedingly feeble at that great distance.

THE MINOR PLANETS

Between Mars and Jupiter, a number of small bodies are known to exist, which have sometimes been dignified by the name of “minor planets.” They have also been called “Planetoids” and “Asteroids.” Special names have been given these individual small bodies--Eros, Ceres, Pallas, Vesta, Juno, etc. Eros passes, upon occasions, very close to our earth; again passing beyond the orbit of Mars. Several hundreds of these smaller planets are now known to exist--as though they were the remnants of some shattered world. These bodies are very small: Ceres, e.g., being about 250 miles in diameter; Pallas, 304 miles; Vesta, 211 miles; while a number of the others are thought to be from 5 to 15 miles in diameter.

ARE THERE OTHER PLANETS?

Inasmuch as some of the planets known to us have only been discovered so lately (relatively) the question has naturally been asked: “Why may there not be other planets, beyond Neptune, still undiscovered?” It is a perfectly legitimate question, and no definite answer to this query can be given. It seems rather improbable that another planet will be discovered. However, it is a conceivable possibility, and M. Flammarion has stated that, in his estimation, such a planet probably exists--gravitating at a distance 48 times as great as the distance between the earth and the sun--that is to say, 7,500 million miles, in an immense orbit which it takes at least 330 years to accomplish. Proof as to the existence of such a planet has not, however, as yet been forthcoming.

THE MOON

The Moon is the Earth’s only satellite, and by far the nearest body in space to our Earth. Many astronomers are inclined to think that the Moon at one time formed a part of the Earth, but was wrenched away from it, leaving a huge cavity, which is now occupied by the Pacific Ocean. The Moon is a cold body, emitting no light or heat of its own; all the light which it seems to shed is entirely reflected light--reflecting the sun’s rays, much as a mirror might reflect them; hence its beautiful silver color.

In round numbers, the Moon is approximately 240,000 miles distant from us in space--the distance varying from 221,600 miles to 252,970 miles--causing a corresponding variation in its apparent diameter and parallax. The circumference of the Moon’s orbit is a little more than a million-and-a-half miles, and it travels through space with the velocity of 2,288.6 miles per hour, or 3,357 feet per second.