EXCENTRICITY

, is the distance between the centres of two circles, or spheres, which have not the same centre.

Excentricity

, in the Old Astronomy, is the distance between the centre of a planet and the centre of the earth.—That the planets have such an Excentricity, is allowed on all sides, and may be evinced from various circumstances; and especially this, that the planets at some times appear larger, and at others less; which can only proceed from hence, that their orbits being Excentric to the earth, in some parts of those orbits the planets are nearer to us, and in others more remote. And as to the Excentricities of the sun and moon, it is thought they are sufficiently proved, both from eclipses, from the moon's greater and less parallax at the same distance from the zenith, and from the sun's continuing longer by 8 days in the northern hemisphere than in the southern one.

Excentricity

, in the New Astronomy, is the distance CS between the sun S and the centre C of a planet's orbit; or the distance of the centre from the focus of the elliptic orbit; called also the Simple or Single Excentricity.

When the greatest Equation of the centre is given, the Excentricity of the earth's orbit may be found by the following proportion; viz, As the diameter of a circle in degrees, Is to the diameter in equal parts; So the greatest equat. of the centre in degrees, To the Excentricity in equal parts. Thus, Greatest equat. of the cent. 1°55′33″=1°.9258333 &c. The diam. of a circ. being 1, its circumf. is 3.1415926. Then 3.1415926 : 1 :: 360° : 114°.5915609 diam. in deg. And 114.5915609 : 1 :: 1.9258333 : 0.016806, the Ex | Hence, by adding this to 1, and subtracting it from 1, gives 1.016806 = AS the aphelion distance, and 0.983194 = BS the perihelion distance. See Robertson's Elem. of Navig. book 5, pa. 286.

Otherwise, thus: Since it is found that the sun's greatest apparent semi-diameter is to his least, as 32′ 43″ to 31′ 38″, or as 1963″ to 1898″; the sun's greatest distance from the earth will be to his least, or AS to SB, as 1963 to 1898; of which, the half dif. is 32 1/2 = CS, and half sum 1930 1/2 = CB; wherefore, as 1930 1/2 : 32 1/2 :: 1 : .016835 = CS the Excentricity, to the mean distance or semi-axis 1; which is nearly the same as before.

The Excentricities of the orbits of the several planets, in parts of their own mean distances 1000, and also in English miles, are as below, viz, the Excentricity of the orbit of

Parts.Miles.
Mercury2107,730,000
Venus7482,000
Earth171,618,000
Mars9313,486,000
Jupiter4823,760,000
Saturn5549,940,000
Georgian47 1/286,000,000

Double Excentricity, is the distance between the two foci of the elliptic orbit, and is equal to double the Single Excentricity above given.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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EVOLUTION
EURYTHMY
EUSTYLE
EXALTATION
EXCENTRIC
* EXCENTRICITY
EXCHANGE
EXCURSION
EXEGESIS
EXHALATION
EXHAUSTIONS