Doubly ionized oxygen: Difference between revisions

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[[File:Oiii-linesp.svg|thumb|right|Emission lines of doubly ionized oxygen: The forbidden lines are shown in green.]]

'''Doubly ionized oxygen''' (also known as '''<nowiki>[O III]</nowiki>''') is a [[forbidden line]] of the [[ion]] [[oxygen|O]]²⁺. It is significant in that it emits light in the green part of the spectrum primarily at the wavelength 500.7 nanometres (nm) and secondarily at 495.9&nbsp;nm. Concentrated levels of <nowiki>[O III]</nowiki> are found in [[diffuse nebula|diffuse]] and [[planetary nebula|planetary]] nebulae. Consequently, narrow [[Dichroic filter|band-pass filter]]s that isolate the 501&nbsp;nm and 496&nbsp;nm wavelengths of light are useful in observing these objects, causing them to appear at higher contrast against the filtered and consequently blacker background of space (and possibly light polluted terrestrial atmosphere) where the frequencies of <nowiki>[O III]</nowiki> are much less pronounced.