LESSON IX.
THE KING OF THE DAY.
“In them hath he set a Tabernacle for the sun,Which is as a bridegroom coming out of his chamber,And rejoiceth as a strong man to run a race,There is nothing hid from the heat thereof.”
“In them hath he set a Tabernacle for the sun,Which is as a bridegroom coming out of his chamber,And rejoiceth as a strong man to run a race,There is nothing hid from the heat thereof.”
“In them hath he set a Tabernacle for the sun,Which is as a bridegroom coming out of his chamber,And rejoiceth as a strong man to run a race,There is nothing hid from the heat thereof.”
“In them hath he set a Tabernacle for the sun,
Which is as a bridegroom coming out of his chamber,
And rejoiceth as a strong man to run a race,
There is nothing hid from the heat thereof.”
—Psalm XIX.
If it should happen that the sun were blotted out, our earth would at once cease to be habitable. Within forty-eight hours the globe would be covered with a deluge of rain, and buried in piles of snow, owing to the condensation of all the moisture in our suddenly chilled atmosphere, while more than Arctic cold would freeze the oceans to their depths. In this reign of cold and darkness all animal and vegetable life would perish. All the planets of our system would share the same fate, and as the light with which they shine is reflected from the sun, they would become invisible, rolling on through space in total darkness.
How far from us is this sun, so important to us as the centre of light, heat, and attraction? Ninety-two millions ofmiles. But how far is that? An engine running thirty miles an hour, without once slacking speed, could go around our globe in thirty-five days. Start it off for a trip to the moon, and with the same speed it would reach there in eleven months. And then send it from the earth to the sun, at an equal rate of travel: year after year it must rush on, until three hundred and fifty-one years were passed before it could reach the sun. But so much faster does light travel than a railroad train, that light comes to us from the sun in eight minutes and nineteen seconds!
“THE LIGHT AND THE NIGHT.”
“THE LIGHT AND THE NIGHT.”
The sun is the centre of our planetary system, and holds all the planets in their proper orbits by the force of his attraction. We have seen in our glance at the asteroid Ceres, that the attraction of gravity depends upon the distance and the weight ormassof the body exercising it. If our earth should suddenly grow lighter it could not hold the moon in its present orbit; if its attractive power over the moon ceased, the moon would go tumbling off into space. The sun exercises immense attractive force by virtue of its enormous mass. If all the planets were put into one pan of a pair of scales, the sun in the other would outweigh them seven hundred times over.Three hundred and fifty thousand such globes as we live upon would be needed to balance the sun.
This gives us some idea of the mass or weight of the sun. What is its size? Our world is nearly eight thousand miles in diameter at the equator; over two hundred and forty thousand miles distant from the earth the moon revolves around it; but if a circle as large as the sun could be drawn, the earth might be placed in the centre, the moon rolled in her proper path around it, and beyond this orbit to the line representing the circumference of the sun would be a distance of nearly two hundred thousand miles more.
This vast orb shines with no borrowed ray. It is a great fountain of burning light which shines now as it shone long before the building of our world began. No light is so powerful and intense as sunlight. A flash of lightning is scarcely seen across a sunny sky; the light of lamps is not visible in strong sunshine; no invented light can approach sunshine in brilliancy. Twenty millions of the brightest stars would not shed upon the earth the radiance poured out by the sun.
According to the nebular hypothesis of Laplace, the sun not only provides the planets with light and heat, but is the source and parent from which they sprung into space. Thus the most distant planets, as Neptune and Uranus, were the ones first thrown off, and the earth, as only in the third remove from its source, is one of the latest of the sun children.
We know that in the far-off ages, when the earth was being built into a habitable globe, the sun shone just as itdoes to-day. We know this from the eyes of fossil animals, which show that they were formed to receive sunlight just as eyes do to-day. Also the petrified rain-marks, of which we spoke in a former chapter, tell the same story; for without the sun there would have been no rain, nor would imprints have dried or baked so rapidly.
The heat and light of the sun are indispensable to the production and growth of all vegetation. Age after age the genial rays of the sun nourished on this earth an improving and enlarging vegetable growth, which on its decay left added soil for generations of plants to come. Thus the sun was not only the parent but the cherishing nurse of our little globe. We have seen that in the coal period of earth-building, the atmosphere of the world was heavily charged with carbonic acid gas, but under the stimulating effects of sunshine, vegetation continually increased, used up most of the carbonic acid gas, and the atmosphere became constantly richer in oxygen,[21]and more and more fitted for the use of animals. Thus we see the sun, as a prudent householder, storing up in the world supplies of coal, and purifying at the same time the air. Meanwhile, by the action of sun rays on the salt, shallow seas, vast salt beds were produced and buried, providing a mineral especially needful to man.
Our dependence upon the sun awakens a desire to know something about the orb itself; but how can a body so intensely bright be studied? Smoked and colored glass plates are used, through which the sun can be observed with comfort, and there are certain occasions when the study ofthis vast, glowing, and distant body can be favorably pursued. These especial occasions favorable to sun-study are during an eclipse, and when the planets Mercury and Venus cross the sun’s disk. Such a crossing is called a transit.
It was once supposed that the sun was no larger than the moon is, and as near to the earth as that planet is; both sun and moon were believed to be much smaller than the earth, and very near to it, and revolving in an orbit about it. To us the sun appears to rise above the horizon, move across the heavens, and sink beneath the horizon, and return after a few hours’ absence to pursue the same path. Meanwhile, the earth does not appear to us to move. This is not the only case in which our eyes deceive us until we call reason to their aid.
When we are on a swiftly moving train of cars, it seems to us that trees, posts, telegraph-poles, go rushing by us, while we remain at rest. Although no one now questions that the earth moves, and that with regard to the earth the sun remains fixed in one place, we still use the language that fits appearances rather than facts, and we say, “the sun rises, the sun sets,” when in truth the earth is merely turning over and over, and so constantly bringing a different part of its surface under the sun’s rays.
As the various planets move about the sun, in paths which we may call concentric circles, or rings set one inside the other, it is evident that there may be occasions when the different planets will come between the sun and some planet with an orbit beyond their own. For instance, Mercury is a planet travelling in a circle around the sun, but a circlesmaller than that in which the earth travels. Mercury may then sometimes pass across the face of the sun at a time when the earth is on the same side of the sun, and in that case we can observe Mercury moving like a little black ball across the glowing front of the King of the Day. To see such an occurrence we must use smoked or darkened glasses, else Mercury would simply be lost in the unshaded splendor of the sunlight. Why is not such a transit of Mercury seen every year? Every year Mercury must cross the disk of the sun, and the reason we do not see a transit yearly is that the orbits of Mercury and the earth differ in plane, and long periods will elapse between the occasions when the sun, Mercury, and the earth come into line thus:
As Venus overtakes the earth in its journey around the sun once every nineteen months, shall we have the benefit of a transit at each time of passing? No; because Venus is usually either above or below the line of the earth’s orbit. But when at long intervals such an event as a transit of Venus does occur, no astronomical incident can be more valuable, because it gives us the best means of measuring the distance between the earth and the sun.
A grand opportunity for studying the sun is afforded by an eclipse. An eclipse of the sun is occasioned by the moon’s passing between the earth and the sun. Children are frequently warned that it is discourteous to pass between a person and the fire or light; our child, the moon, happily for us, often passes between us and our fire, the sun, and on the fortunate occasions when this can be observed out comethe glasses for sun-study. As the moon revolves about the earth, she sometimes stands between the sun and the earth. When the moon passes between us and the sun on a clear day, between sunrise and sunset, the day grows dark, a twilight comes over the world, and continues until the moon has crossed the disk of the sun.
How can so small a body as the moon obscure so great a body as the sun, and how can the moon pass in seven minutes across a disk nearly a million of miles in extent? All this can be explained by the nearness of the moon to our globe, and consequently the moon’s great distance from the sun. Any one of us can hide the sun from us by a dinner-plate, or even a dime, if we hold it close enough to our eyes. So we can move a dinner-plate across the disk of the sun, by one sweep of the arm. All depends upon the nearness to ourselves of the screen used. Now as the moon is so near us in time of eclipse, she hides the sun from us; the eclipse may last for an hour, but will be total only for a few moments.
Every year there must be more than one eclipse of the sun. The greatest number possible in a year is five, the least two; but these will not all be visible from the same part of the globe.
Astronomers call an eclipse partial when the moon passes over one or the other side of the sun’s disk. An annular or ring eclipse is one where the moon is at such a distance from the earth, that she hides only the central part of the sun’s disk, while around the dark shadow thus cast appears a ring of splendid light. A total eclipse of the sun is wherethe moon is so near us that she hides the entire face of the sun. This can happen only at long intervals for any given locality. Thus, when there is a total eclipse of the sun visible from New York City, it may be hundreds of years before such an eclipse is again seen from there.
When the sun is in total eclipse a glorious halo of clear light called a corona, or crown, rays out on all sides behind the black body of the moon. Horns, cones, and streamers of violet, scarlet, orange, and pink light rise up from this crown, and seem to toss and whirl like clouds in a storm.
In the careful study of the sun with telescopes, it has been found that there are spots on its surface, which look as if the outer portion of the sun were torn. Now by watching these spots a very wonderful fact has been discovered. What do you think that is? Why, that the sun turns over on its axis, as the earth does. But while the earth rotates once in twenty-four hours, it takes the huge sun about twenty-five days to turn around once.
Not only is the sun turning over on its axis, but it has a great path along which it travels in space, and as it goes on it draws with it all the planets and satellites of our system, each held in its proper path by the great force of the sun’s attraction. Thus we have learned that from the sun these great globes, the planets, were thrown off into space, by tangental force, and lest they should go too far away they are held in their paths by his strong attractive force.
FOOTNOTES:[21]Nature Reader, No. 3, pp. 40-42.
[21]Nature Reader, No. 3, pp. 40-42.
[21]Nature Reader, No. 3, pp. 40-42.