In the Helix Nebula APOD thread from October 4, 2012, Art wrote:
neufer wrote:http://en.wikipedia.org/wiki/Forbidden_mechanism wrote:
<<In physics, a forbidden mechanism or forbidden line is a spectral line emitted by atoms undergoing nominally "forbidden" energy transitions not normally allowed by the selection rules of quantum mechanics. Forbidden lines of nitrogen ([N II] at 654.8 and 658.4 nm), sulfur ( at 671.6 and 673.1 nm), and oxygen ([O II] at 372.7 nm, and [O III] at 495.9 and 500.7 nm) are commonly observed in astrophysical plasmas. These lines are extremely important to the energy balance of such things as planetary nebulae and H II regions. Also, the forbidden 21-cm hydrogen line is of the utmost importance for radio astronomy as it allows very cold neutral hydrogen gas to be seen.>>
The color that Art chose to illustrate OIII at 495.9 and 500.7 nm is #008080, which I interpret as no red, but equal amounts of green and blue.
I'd like a comment here. Should OIII emission be regarded as the perfect shade of cyan?