In geometry, the semi-minor axis (also semiminor axis) applies to ellipses and hyperbolas.
Ellipse
The semi-minor axis of an ellipse is one half of the minor axis, running from the center, halfway between and perpendicular to the line running between the foci, and to the edge of the ellipse. The minor axis is the longest line that runs perpendicular to the major axis.
A parabola can be obtained as the limit of a sequence of ellipses where one focus is kept fixed as the other is allowed to move arbitrarily far away in one direction, keeping l fixed. Thus a and b tend to infinity, a faster than b.
Hyperbola
The semi-minor axis of a hyperbola is the distance from a top, along the tangent line, to each asymptote; if this is in the y-direction it is b in this equation of the hyperbola:
It is related to the semi-major axis through the eccentricity, as follows:
e., the axis of a cone, that is, the straight line joining the vertex and the center of the base; the axis of a circle, any straight line passing through the center.
The two axes of the ellipse are the {major axis} and the {minor axis}, and the two axes of the hyperbola are the {transverse axis} and the {conjugate axis}.
{Axis of the} {equator, ecliptic, horizon} (or other circle considered with reference to the sphere on which it lies), the diameter of the sphere which is perpendicular to the plane of the circle.
A semimajor axis is one half the major axis: the line segment from the center, through a focus, and to the edge of the ellipse.
The constant a equals the length of the semimajor axis; the constant b equals the length of the semiminoraxis.
The shape of an ellipse is usually expressed by a number called the eccentricity of the ellipse, conventionally denoted e (not to be confused with the mathematical constant e).
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