Ellipsoid
An ellipsoid is a shape like a sphere, but it may be longer in one or more directions, like a rugby ball. It is the 3 dimensional analogue of an ellipse.
The Earth is shaped slightly like an ellipsoid. Its shape is called an oblate spheroid. An ellipsoid shaped like the Earth, called a reference ellipsoid, is often preferred to the geoid because it makes calculations simpler.
Ellipsoid Media
Examples of ellipsoids with equation x2a2 + y2b2 + z2c2 = 1: Template:Ubl*
Plane section of an ellipsoid
Plane section of an ellipsoid (see example)
Plane section of the unit sphere (see example)
Pins-and-string construction of an ellipse:*Expression error: Unrecognized punctuation character "'"., length of the string (red)
Pins-and-string construction of an ellipsoid, blue: focal conics
Determination of the semi axis of the ellipsoid
Top: 3-axial Ellipsoid with its focal hyperbola.*Bottom: parallel and central projection of the ellipsoid such that it looks like a sphere, i.e. its apparent shape is a circle
ellipsoid as an affine image of the unit sphere
Artist's conception of Haumea, a Jacobi-ellipsoid dwarf planet, with its two moons
