Plate 1.
II. PHYSICAL AND CHEMICAL CONDITION OF THE SUN.
Physical Condition of the Sun.
143. The Sun Composed mainly of Gas.—It is now generally believed that the sun is mainly a ball of gas, or vapor, powerfully condensed at the centre by the weight of the superincumbent mass, but kept from liquefying by its exceedingly high temperature.
The gaseous interior of the sun is surrounded by a layer of luminous clouds, which constitutes its visible surface, and which is called its photosphere. Here and there in the photosphere are seen dark spots, which often attain an immense magnitude.
These clouds float in the solar atmosphere, which extends some distance beyond them.
The luminous surface of the sun is surrounded by a rose-colored stratum of gaseous matter, called the chromosphere. Here and there great masses of this chromospheric matter rise high above the general level. These masses are called prominences.
Outside of the chromosphere is the corona, an irregular halo of faint, pearly light, mainly composed of filaments and streamers, which radiate from the sun to enormous distances, often more than a million of miles.
In Fig. 161 is shown a section of the sun, according to Professor Young.