conic sections
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conic sections
(kon -ik) (conics) A family of curves that are the locus of a point that moves so that its distance from a fixed point (the focus) is a constant fraction of its distance from a fixed line (the directrix). The fraction, e , is the eccentricity of the conic. The value of the eccentricity determines the form of the conic. If e is less than 1 the conic is an ellipse. A circle is a special case of this with e = 0. If e = 1 the conic is a parabola and if e exceeds 1 the conic is a hyperbola.These curves are known as conic sections because they can be obtained by taking sections of a right circular cone at different angles: a horizontal section gives a circle, an inclined one an ellipse, one parallel to the slope of the cone is a parabola, and one with an even greater inclination is a hyperbola (see illustration). Conics are important in astronomy since they represent the paths of bodies that move in a gravitational field. See also orbit.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
Conic sections
Circle, ellipse, parabola, and hyperbola; all produced by cutting a plane through a cone at different angles.

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