semiminor axis

geometry

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July 13, 2026

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The semiminor axis is half the length of the minor axis of an ellipse. The minor axis is a line segment that passes through the center of the ellipse, is perpendicular to the major axis, and connects two points on the ellipse.12

An ellipse is a closed curve defined by two foci. The sum of the distances from any point on the ellipse to the two foci is constant. The major axis is the longest diameter of the ellipse, passing through both foci, while the minor axis is the shortest diameter, perpendicular to the major axis at the ellipse's center. The semiminor axis is crucial in defining the shape and size of an ellipse, particularly in astronomical contexts like planetary orbits.21

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geoid
…radius for Earth) and a semiminor axis (polar radius), or the flattening. Flattening (f) is defined as the difference in magnitude between the semimajor axis (a) and the semiminor axis (b) divided by the semimajor axis, or f = (a − b)/a. For Earth the semimajor axis and semiminor axis…
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…radius for Earth) and a semiminor axis (polar radius), or the flattening. Flattening (f) is defined as the difference in magnitude between the semimajor axis (a) and the semiminor axis (b) divided by the semimajor axis, or f = (a − b)/a. For Earth the semimajor axis and semiminor axis…
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