THE SUN

The Sun is the center of our solar (sun) system; it is the great giver of light and heat, without which life upon our planet would soon become extinct. It is an immense body, more than a million times the size of our earth. In fact, its radius is nearly twice the distance of the moon from the earth! The mass of the Sun is 332,000 times that of the earth. It gives 600,000 times as much light as the full moon. The energy radiated per square yard from the Sun is equivalent to 140,000 horse power. The heat radiated by the sun would melt a layer of ice 4,000 feet thick every hour, all over its surface. Various estimates of the amount of heat upon the surface have been made, but these do not agree,—figures all the way from 10,000° F. to 180,000° F. having been given. Certain it is that its internal heat is terrific, and there is every indication that this heat has been more or less constant for millions of years in the past. No purely physical theories of its heat are at all satisfactory. The ultimate nature and source of the sun’s heat are unknown—though various theories have been advanced by way of explanation. I have discussed this question at some length, however in my little book in the present series, “New Discoveries in Science,” to which the reader is referred. (“What Keeps the Sun Hot?”)

The nature and constitution of the sun have, of course, been studied intensively for many years by astronomers. The apparent surface of the sun is called the “photosphere” (light surface). It is the part that gives forth most of the light and heat. Above the photosphere lies a sheet of gas, probably from 500 to 1,000 miles thick, called the “reversing layer,” which is cooler than the photosphere. Outside the photosphere is another layer of gas, from 5,000 to 10,000 miles deep, called the “chromosphere” (cooler sphere). The outermost portion of the Sun is the “corona” (crown). It is a halo of pearly light surrounding the sun, but it cannot be seen except during a total eclipse. It is of irregular form, and gradually fades out into the blackness of space at a distance of from 1,000,000 to 3,000,000 miles. This must not be confounded with the so-called “prominences,” which are vast eruptions of flame, spurting out from the sun’s surface, and extending into space for enormous distances—perhaps half a million miles! These also travel with enormous velocity—five or six hundred miles per second. The earth would appear an insignificant speck of dust, in this vast, roaring furnace of flame!

Of late years, the question of the so-called “sun spots” has aroused a great deal of interest, partly by reason of the fact that they apparently affect electrical and magnetic conditions upon the earth. These “spots” seem to reappear at stated intervals, and about every eleven years reach their maximum intensity, (The period of the revolution of the sun on its own axis has been estimated by their study.)

Although the sun-spots were studied before the eighteenth century, it is only within the past few years that the significance of these enormous spots has become known. For long it was thought that they were merely the great volcanoes of the sun; centers of great heat, generated by the glowing, fiery gases of the sun. In 1908, however, Prof. Hale demonstrated that the sun-spots acted as attraction centers, which drew towards them the hydrogen of the solar atmosphere. “Subsequently, it was found that these spots are the seats of great cyclones, in which cool hydrogen gas is set whirling and is sucked down in the great mælstrom of the Sun, rushing into the center of the spot at the rate of 60 miles a second. Consequently the spots are the center of great solar disturbances, which are of an electromagnetic nature.” From this it was concluded (1) that the spots are cooler than the surrounding area; (2) they are centers of violent cyclones; and (3) they are magnetic fields of great intensity. The connection of sun-spots with our weather, and the relation of one to the other, have also been studied within the past few years.