Effective radius

The effective radius R _e includes half of all light emitted by an object.

The effective radius , the effective radius or half-light radius describes the radius or , in the half of the luminance of an astronomical object is emitted: ${\displaystyle R_{e}}$ ${\displaystyle R}$ ${\displaystyle r}$ ${\displaystyle I}$

${\displaystyle \int _{0}^{R_{e}}I(R)\cdot r\cdot dr={\frac {1}{2}}\cdot \int _{0}^{\infty }I(R)\cdot r\cdot dr}$

The effective radius is used to describe star clusters and galaxies , especially to calculate the course of the surface brightness of a bulge or an elliptical galaxy with the help of the De Vaucouleurs formula .

This measured variable depends on the observation instrument used, because with smaller instruments the outer areas of the astronomical object can be below the limit brightness .

See also

• Sérsic profile

literature

• Peter Schneider: Introduction to Extragalactic Astronomy and Cosmology . Springer Verlag, Berlin 2005, ISBN 3-540-25832-9 .