Mean radius

A sphere (top), rotational ellipsoid (left) and triaxial ellipsoid (right)

The mean radius (or sometimes the volumetric mean radius) in astronomy is a measure for the size of planets and small Solar System bodies. Alternatively, the closely related mean diameter (), which is twice the mean radius, is also used. For a non-spherical object, the mean radius (denoted or ) is defined as the radius of the sphere that would enclose the same volume as the object.[1] In the case of a sphere, the mean radius is equal to the radius.

For any irregularly shaped rigid body, there is a unique ellipsoid with the same volume and moments of inertia.[2] The dimensions of the object are the principal axes of that special ellipsoid.[3]

  1. ^ Leconte, J.; Lai, D.; Chabrier, G. (2011). "Distorted, nonspherical transiting planets: impact on the transit depth and on the radius determination" (PDF). Astronomy & Astrophysics. 528 (A41): 9. arXiv:1101.2813. Bibcode:2011A&A...528A..41L. doi:10.1051/0004-6361/201015811.
  2. ^ Milman, V. D.; Pajor, A. (1987–88). "Isotropic position and inertia ellipsoids and zonoids of the unit ball of a normed n-dimensional space" (PDF). Geometric Aspects of Functional Analysis. Lecture Notes in Mathematics. Vol. 1376. Berlin, Heidelberg: Springer. pp. 65–66. doi:10.1007/BFb0090049. ISBN 978-3-540-51303-2.
  3. ^ Petit, A.; Souchay, J.; Lhotka, C. (2014). "High precision model of precession and nutation of the asteroids (1) Ceres, (4) Vesta, (433) Eros, (2867) Steins, and (25143) Itokawa" (PDF). Astronomy & Astrophysics. 565 (A79): 3. Bibcode:2014A&A...565A..79P. doi:10.1051/0004-6361/201322905.

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