The Solar System

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General Books, 2009 - 100 pages
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1846 edition. Excerpt: is only sixteen degrees from the sun; while at others, it is nearly twenty-nine degrees distant. Its eccentricity, or the distance of the sun from the centre of its orbit, is above seven millions of miles; which is about the one-tenth part of the diameter of its orbit; and this orbit is inclined to the ecliptic, or the plane of the earth's orbit, in an angle of seven degrees, so that it is sometimes this number of degrees above the level of the ecliptic, and at other times as much below it. The density of this planet is greater than that of any other planet of the system. It has been estimated to be nearly twice the density of the earth, that is about nine times the density of water, or nearly equal to that of lead. Such conclusions are deduced from the laws of gravitation, by which all the planets are directed in their motions. Transits of Mercury.--At certain periods, this planet is observed to pass across the sun's disk, like a small dark spot. This can happen only at the time of its inferior conjunction with the sun--when it is nearest to the earth--when its enlightened side is turned towards the sun, and its dark hemisphere is turned directly towards the earth; and when the earth, Mercury, and the sun are nearly in one straight line. This passage of Mercury across the solar disk, is called its transit, and is considered by astronomers as an interesting phenomenon. If the orbit of this planet were in the same plane with that of the earth, it would transit the sun's disk, at every inferior conjunction, or three or four times every year. But as its orbit is inclined to the ecliptic, a transit can happen only when it comes to the inferior conjunction, at the time when it is at or near its nodes, or the points where it crosses the ecliptic, ...

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