Though the sun appears to us merely as a circular disk, yet he is a _spheroid_, higher under his equator than about his poles. The deception arises from this; that all the parts of his surface are equally luminous, and consequently there is nothing which can suggest to us, at the great distance he is from the earth, that the central parts are more prominent than the sides, although in reality, they are nearer by half a million of miles. This luminous body is supposed to be 886,473 English miles in diameter, about 2,700,000 in circumference, in solid bulk 24,000,000 times as big as the moon, and 1,384,462 times as big as the earth, and its superficies in square miles, about 2,236,603,000,000. This _magnitude_ of the sun may appear exaggerated; for our eyes can discover nothing so large as the earth which we inhabit; and as to this alone we compare the sun, so we are tempted to believe the testimony of sense rather than our reason. But what confirms this prodigious size, is his visible magnitude, notwithstanding the vastly remote point which he occupies in space. And, concerning this subject, no doubt can remain, if we admit the calculations of astronomers, which are made on principles indubitably correct. The sun does not appear large; but this is owing to his _distance_ from the earth, which is 95,513,794 miles: this is so prodigious, that a cannon-ball, which is known to move at the rate of eight miles in a minute, would be something more than twenty-two years in going from the earth to the sun. If a spectator were placed as near to any of the fixed stars as we are to our sun, he would see our sun as small as we see a common star, divested of its circumvolving planets; and in numbering the stars he would reckon it one of them. But the earth’s orbit being an ellipse, the sun is not always at an equal distance from it. When he is in his apogee, that is, furthest from the earth, the sun is full two millions of miles further from us than when he is in his perigee, or nearest the earth: nevertheless, we feel greater heat than when he is in our winter. The difference of temperature between summer and winter does not depend chiefly upon our nearness to the sun, but upon the following causes. 1. In summer, the solar rays strike upon the earth more perpendicularly than in winter, and therefore they act with greater force than when they strike it obliquely. 2. The rays of the sun coming more perpendicularly in summer than in winter, have less of the atmosphere to pass through. 3. In the summer, the sun continues a longer time above the horizon than below it; and consequently there is time for the earth to accumulate a greater portion of heat than in the days of winter. We know, in the longest days, that the sun to us is above the horizon 16 hours; whereas, in the shortest days, it is not more than 8 hours visible.[114]