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A truly dark sky has a surface brightness of 2 × 10 −4 cd m −2 or 21.8 mag arcsec −2. [9] [clarification needed] The peak surface brightness of the central region of the Orion Nebula is about 17 Mag/arcsec 2 (about 14 milli nits) and the outer bluish glow has a peak surface brightness of 21.3 Mag/arcsec 2 (about 0.27 millinits). [10]
An image of NGC 45, a low surface brightness spiral galaxy, by GALEX. UGC 477 is located over 110 million light-years away in the constellation of Pisces. [1]A low-surface-brightness galaxy, or LSB galaxy, is a diffuse galaxy with a surface brightness that, when viewed from Earth, is at least one magnitude lower than the ambient night sky.
In contrast, the term brightness in astronomy is generally used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and the distance between the object and observer, and also on any absorption of light along the path from object to ...
In visible light, the galaxy exhibits an overall bluish color and as it is relatively dim for a galaxy of its size, it is classified as a low surface brightness galaxy (LSB). [2] [3] NGC 5866B is located relatively close in the sky to the more well-known NGC 5907 (Splinter Galaxy) and NGC 5866 (Spindle Galaxy). [4]
Brightness refers to how much light appears to shine from something. This is a different perception than lightness, which is how light something appears compared to a similarly lit white object. [2] The adjective bright derives from an Old English beorht with the same meaning via metathesis giving Middle English briht.
UGC 6614 is classified as a low surface brightness (LSB) galaxy. [3] [4] [5] The galaxy is nearly face-on and has a ring-like feature around its bulge, [6] with distinctive extended spiral arms. [7] The bulge of UGC 6614 is found to be red, similar to those of S0 and other elliptical galaxies, hinting at the existence of an old star population. [8]
An object's surface brightness is its brightness per unit solid angle as seen in projection on the sky, and measurement of surface brightness is known as surface photometry. [9] A common application would be measurement of a galaxy's surface brightness profile, meaning its surface brightness as a function of distance from the galaxy's center.
(The S 10 unit is defined as the surface brightness of a star whose V-magnitude is 10 and whose light is smeared over one square degree, or 27.78 mag arcsec −2.) The total sky brightness in zenith is therefore ~220 S 10 or 21.9 mag/arcsec² in the V-band. Note that the contributions from Airglow and Zodiacal light vary with the time of year ...