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A PHOTOGRAPH OF THE SUN, SHOWING THE CLOUDS OF FIERY VAPOR WHICH SURROUND IT

Dimensions of the Sun. The sun appears to human vision as a brilliant globe of a little more than half a degree in diameter. It is about the same apparent size as the moon, since the size of the sun is to that of the moon very nearly in the same proportion as their relative distances from the earth. In reality, however, the sun is a gigantic orb, so huge that if the earth were at its center the whole orbit of the moon would lie well within its circumference. The diameter of the sun is about 866,500 miles.

The mass of the sun is about 332,000 times that of the earth, but its specific gravity is only about a quarter that of the earth, 1.41, if that of water be taken as unity. The mean distance of the sun from the earth is about 92,800,000 miles; but, as the earth’s orbit is not circular but elliptic, this distances varies by about 3,000,000 miles, being smallest in January and greatest in July.

The Physical Condition of the sun is very different from that of the earth, though we know it is composed of very similar materials. The white-hot surface that we see, called the photosphere, is believed to be largely a shell of highly heated metallic vapors surrounding the unseen mass beneath. Dark spaces seen in the photosphere are known as sun-spots, and these are often surrounded by brighter patches, termed faculæ. Above the photosphere a shallow envelope of gases, rising here and there into huge prominences, and known as the chromosphere, is seen in red tints when the sun is totally eclipsed. Beyond the chromosphere, there is also seen, at the same time, a faint but far more extensive envelope called the corona.

This diagram illustrates the theory that sun-spots are formed by fragments struck from Saturn’s rings (which are in themselves nothing more than a great meteoric swarm) by the swarm of meteors known as the Leonids, which fragments fall into the solar furnace at a speed of four hundred miles a second.

The sun’s rays supply light and heat not only to the earth, but also to the other planets which revolve round it. Its attraction confines these planets in their orbits and controls their motions.