• For planet
Earth, which can be approximated as an oblate spheroid with radii and , the mean radius is R=\left((6378.1~\text{km})^{2}\cdot6356.8~\text{km}\right)^{1/3}=6371.0~\text{km}. The equatorial and polar radii of a planet are often denoted r_{e} and r_{p}, respectively. • The
asteroid 511 Davida, which is close in shape to a tri-axial ellipsoid with dimensions , has a mean diameter of D=(360~\text{km}\cdot294~\text{km}\cdot254~\text{km})^{1/3}=300\text{ km}. • Assuming it is in hydrostatic equilibrium, the dwarf planet
Haumea has dimensions 2,100 × 1,680 × 1,074 km, resulting in a mean diameter of D=\left(2100~\text{km}\cdot1680~\text{km}\cdot1074~\text{km}\right)^{1/3}=1559~\text{km}. The
rotational physics of
deformable bodies predicts that over as little as a hundred days, a body rotating as rapidly as Haumea will have been distorted into the equilibrium form of a tri-axial ellipsoid. == See also ==