Editing Surface brightness (section)

==Examples==
A truly dark sky has a surface brightness of {{val|2|e=-4}} &nbsp;cd&nbsp;m<sup>−2</sup> or 21.8&nbsp;mag&nbsp;arcsec<sup>−2</sup>.<ref name="Crumey">Based on the equivalence 21.83&nbsp;mag&nbsp;arcsec<sup>−2</sup> = {{val|2|e=-4}} &nbsp;cd&nbsp;m<sup>−2</sup>, from description of a "truly dark sky", Section 1.3 of Crumey, A. (2014). [http://mnras.oxfordjournals.org/content/442/3/2600.full.pdf+html Human contrast threshold and astronomical visibility.] MNRAS 442, 2600–2619.</ref>
{{Clarify|date=February 2018|reason=A surface brightness in mag/arcsec^2 is only meaningful if a filter band or wavelength band is specified. Also useful to specify Vega or AB mag.}}

The peak surface brightness of the central region of the [[Orion Nebula]] is about 17 Mag/arcsec<sup>2</sup> (about 14 [[milli]][[nit (unit)|nits]]) and the outer bluish glow has a peak surface brightness of 21.3 Mag/arcsec<sup>2</sup> (about 0.27 millinits).<ref>{{cite web
 |url        = http://www.clarkvision.com/astro/surface-brightness-profiles/introduction.html
 |title      = Surface Brightness of Deep Sky Objects
 |date       = 2004-03-28
 |first      = Roger
 |last       = Clark
 |access-date = 2013-06-29
}}. The conversion to nits is based on 0 magnitude being 2.08 microlux.</ref>