# eccentricity

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## eccentricity,

in astronomy: see orbit**orbit,**

in astronomy, path in space described by a body revolving about a second body where the motion of the orbiting bodies is dominated by their mutual gravitational attraction.

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## eccentricity

Symbol:*e*. A measure of the extent to which an elliptical orbit departs from circularity. It is given by the ratio

*c*/2

*a*where

*c*is the distance between the focal points of the ellipse and 2

*a*is the length of the major axis. For a circular orbit

*e*= 0. The planets and most of their satellites have an eccentricity range of 0–0.25 (see table). Many comets and some of the asteroids and planetary satellites have very eccentric orbits. The eccentricity of an orbit varies over a long period due to changing gravitational effects: that of the Earth's orbit varies between about 0.005 to 0.06 in a period of about 100 000 years. See also conic sections.

## Eccentricity

in a conic section, a number equal to the ratio of a point’s distance from the focus to its distance from a directrix. The eccentricity characterizes the shape of a conic section. For example, two conic sections that have the same eccentricity are similar. The eccentricity of an ellipse is less than unity, that of a hyperbola is greater than unity, and that of a parabola is equal to unity. For the ellipse and hyperbola, the eccentricity may be defined as the ratio of the distances between the foci to the longer or real axis.

## eccentricity

[‚ek·sən′tris·əd·ē] (mathematics)

The ratio of the distance of a point on a conic from the focus to the distance from the directrix.

(mechanics)

The distance of the geometric center of a revolving body from the axis of rotation.

## Eccentricity

Addams Familyweird family, presented in grotesque domesticity. [TV: Terrace, I, 29]

travels with set of

*Encyclopaedia Britannica*to settle disputes. [Am. Lit.: “Percy” in*Stories*, 634–644]odd but harmless old gentleman. [Br. Lit.:

*David Copperfield]*veterinarian who talks to animals. [Children’s Lit.:

*Dr. Doolittle*]“ancient” ward in Chancery. [Br. Lit.:

*Bleak House*]outlandish dresser who pointedly doesn’t eat meat. [Children’s Lit.:

*The Growing Summer*, Fisher 124–127]jilted bride turns into witchlike old woman. [Br. Lit.:

*Great Expectations*]outrageous, rebellious, imaginative child. [Children’s Lit.:

*Pippi Longstocking*]individualist; only girl “out of line.” [Children’s Lit.:

*Madeline*, Fisher, 196]delightfully pixilated old woman manages to exploit the Parisian exploiters. [Fr. Lit.:

*The Madwoman of Chaillot*, Benét, 618]jolly “conformist” who understands anything but the obvious. [Br. Lit.:

*Pickwick Papers*]English nanny who practises levitation, flies up chimneys, etc. [Children’s Lit.:

*Mary Poppins*, Fisher, 218]behaved queerly to share outcasts’ contempt. [Christian Hagiog.: Attwater, 311]

## eccentricity

**1.**deviation from a circular path or orbit

**2.**a measure of the noncircularity of an elliptical orbit, the distance between the foci divided by the length of the major axis

**3.**

*Geometry*a number that expresses the shape of a conic section: the ratio of the distance of a point on the curve from a fixed point (the focus) to the distance of the point from a fixed line (the directrix)

**4.**the degree of displacement of the geometric centre of a rotating part from the true centre, esp of the axis of rotation of a wheel or shaft