To assign a magnitude to astronomical objects that are not point sources, such as galaxies and nebulas, astronomers treat them as if all the light from such an object to the telescope came from a point. So the Orion nebula, whose integrated magnitude is 6, doesn't look as bright as a magnitude 6 star.
If light from all the stars (excluding the sun) were combined in a single star, it would have an apparent magnitude of -6.7, much less than the full moon.
The range of brightness of everything seen in the sky before the 1990's can be summed up in two gigantic leaps of apparent magnitude: the sun is about 25 magnitudes (10¹⁰) brighter than the brightest star, Sirius, and Sirius is 25 magnitudes brighter than the faintest star that can be photographed by the 200-inch telescope on Mt. Palomar.
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Last revised: 8 March 2008.