Oblate
An oblate
spheroid is a
rotationally symmetric ellipsoid having a polar axis shorter than the diameter of the equatorial circle whose plane bisects it. It can be formed by rotating an
ellipse about its
minor axis, forming an equator with the end points of the
major axis. As with all ellipsoids, it can also be described by the lengths of three mutually perpendicular principal axes, which are in this case two arbitrary equatorial
semi-major axes and one
semi-minor axis.
The oblate spheroid is interesting because it is the approximate shape of many
planets and celestial bodies, including the
Earth.
Encyclopedia
An
oblate spheroid is a
rotationally symmetric ellipsoid having a polar axis shorter than the diameter of the equatorial circle whose plane bisects it. It can be formed by rotating an
ellipse about its
minor axis, forming an equator with the end points of the
major axis. As with all ellipsoids, it can also be described by the lengths of three mutually perpendicular principal axes, which are in this case two arbitrary equatorial
semi-major axes and one
semi-minor axis.
The oblate spheroid is interesting because it is the approximate shape of many
planets and celestial bodies, including the
Earth. It is therefore the geometric figure most used for defining reference ellipsoids, upon which cartographic and geodetic systems are based.
- For a discussion of the physics that determines the shape of a spinning celestial body, see Equatorial bulge
The
aspect ratio,
b:
a, is the ratio of the polar to equatorial lengths, while the
flattening,
f, is the ratio of the equatorial-polar length difference to the equatorial length:
These are just two of several different parameters used to define an ellipse and its solid body counterparts, all of which are ultimately trigonometric functions of the ellipse's
modular angle, or
angular eccentricity.
See also
External links
