Flattening

(Redirected from Ellipticity)

Categories: Astronomy | Geodesy | Geophysics

The flattening, ellipticity, or oblateness of an oblate spheroid is the relative difference between its equatorial radius a and its polar radius b:

<math>f =\frac{a - b}{a}</math>

• The flattening of the Earth is 1:298.25275 (which corresponds to a radius difference of 21.385 km of the Earth radius 6378.135 - 6356.75 km) and would not be realized visually from space,
• whereas the flattening of Jupiter is 1:16 (which can be seen even in a small telescope, or that of Saturn ~ 1:10
• and of the Sun less than 1:1000.

The amount of flattening depends on

• the relation between gravity and centrifugal force, and in detail on
• size and density of the celestial body - see Figure of the Earth, last chapter
• the rotation of the planet or star
• the elasticity of the body.

See also: Astronomy, planetography, Earth rotation, gravity fieldde:Abplattung