General:The state or quality of being bright.
Deraxšandegi, from deraxš, present stem of deraxšidan "to shine," → bright, + -andé adjective suffix + -gi noun suffix.
Fr.: distribution de brillance
A statistical distribution of the brightness of an astronomical extended object.
Fr.: température de brillance
In radio astronomy, the temperature of a source calculated on the assumption that it is a blackbody emitting radiation of the observed intensity at a given wavelength. → antenna temperature.
Fr.: brillance intrinsèque
The brightness of an object, such as a star, that is not affected by interstellar absorption and independent of distance.
low surface brightness galaxy (LSBG)
kahkešân bâ deraxšandegi-ye ruye-yi-ye kam
Fr.: galaxie à faible brillance de surface
A member of a particularly faint population of galaxies with a central → surface brightness below the brightness of the background sky. The central regions of many of them resemble a → dwarf galaxy, but most of the mass is contained in a large gaseous disk of low density that is observable only with long-exposure optical images or at radio wavelengths. Some are as massive as a large → spiral galaxy, for example Malin 1. The proportion of LSBGs relative to normal galaxies is unknown. They may however represent a significant fraction of mass in the Universe. LSBGs are thought to be primitive systems because they have total masses similar to normal galaxies, but have typically converted less than 10% of their gas into stars. Spiral LSBGs do not obey → Freeman's law.
Fr.: brillance du ciel
Atmospheric (→ airglow, → auroral emission, → artificial light) or extraterrestrial (→ scattered → sunlight from Moon, scattered → starlight, → interplanetary dust) foreground light that → interferes with → observations.
deraxandegi-ye ruyé, ~ ruye-yi
Fr.: brillance de surface
The brightness of an extended object, such as a planet, nebula, galaxy, or the sky background, expressed as magnitudes per unit area (usually square arc second). Surface brightness is calculated by dividing the object's magnitude by its size (→ isophotal radius).