Holmberg radius

Holmberg radius

(holm -berg) The length of the semimajor axis of a galaxy down to a surface brightness of 26.5 magnitudes per square arc second, expressed either in arc minutes, or if the distance to the galaxy is known, in kiloparsecs. It is a useful measurement of the visible size of the galaxy.

Holmberg radius

[′hōm‚bərg ‚rād·ē·əs]
(astronomy)
The radius of an external galaxy at which the surface brightness is such that the light emitted from one square arc-second equals that from a star of magnitude 26.6.