Sun

(sün.) [Deriv. uncertain.) (Ast.) The central and controlling orb of the planetary system, the source of light and heat to this earth and all the other globes which form that system. This splendid luminary is 96,000,000 of miles distant from the earth; a cannonball travelling at a uniform velocity of 1,600 feet in a second, would require ten years to reach it from the earth. Its diameter is 892,000 miles; its ma is 354,936 times that of the earth, and 800 times greater than the aggregate of the ma es of all the planets and satellites; its density is about one-fourth that of the earth; a body which, at the earth's surface, would weigh one pound, would on that of the sun weigh 27.9 lbs.; and an ordinary man would be crushed to atoms by his own weight. The sun revolves on its axis in about 25 days; which is ascertained by means of the spots or ma culæ on his surface; and his equator is inclined to the ecliptic at an angle of about 7° 20′. The spots are subject to change; they vanish and reappear; one has been observed covering an area of 1,520 millions of sq. m., that is, a space thirty times greater than the whole surface of the earth. There are several hypotheses regarding them, but none which is satisfactory. Some imagine that the luminous atmosphere of the sun is at a great distance from its ma ; and that the calorific rays are so intercepted by clouds as to render it habitable; but there can be little doubt that a most intense heat prevails at its surface. It is also supposed that the heat and light constantly pa ing off may gradually diminish its bulk. It is highly probable that the sun has a proper motion in space, though some centuries of observation may be required to detect its laws. Astronomers have lately seen reason to think that the mean distance of the earth from the sun is not so great by four millions of miles as was formerly supposed. This distance is now put down at 91,328,000 miles. Various other numerical changes become nece ary. Thus the circumference of the earth's orbit becomes 599,194,000 miles; and her mean hourly velocity 65,460 miles. The diameter of the sun is 850,100 miles. The numerical expre ions for the distances, velocities, and dimensions of all the other planetary bodies will require corresponding correction. The fa culæ of the sun are bright streaks commonly seen in the neighborhood of spots which are approaching the sun's limb. Secchi says, that though they appear bright in this position, they are not in reality brighter than the centre of the sun. The same eminent solar observer believes them to be immense waves of matter indicating the disturbance to which the formation of a spot is due. Me rs. De La Rue, Stewart, and Loëwy, consider the fa culæ as probably consisting of solid or liquid bodies slowly subsiding in a gas eons medium. From their falling behind the spots it is inferred that they were originally lifted above the general level, and in the proce fell behind because coming into regions of more rapid rotation. [s. 868]