An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A three-dimensional geometric figure resembling a flattened sphere. It is generated by rotating an ellipse around one of its axes.

From → ellipse + → -oid.

An ellipsoid used in describing the motion of a rotating rigid body. It is stationary with respect to the rotating body, and is determined by the body's moments of inertia.

→ ellipsoid; → inertia.

A mathematically defined surface that approximates the Earth's shape, which is basically a sphere "flattened" at its poles. The length of one of the axes at the Equator is chosen so that the ellipsoid coincides at this latitude with the mean sea level. It is the first-order definition of the non-spherical shape of the Earth as an ellipsoid of revolution. To first order, it accounts for over 90% of the → geoid.

→ reference; → ellipsoid.