Talk:H II region
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Would "forbidden lines" be the same as "absorption lines"? I here that term a lot when speaking of stellar spectra, but I've never heard them called "forbidden". -- John Owens 15:08 Apr 7, 2003 (UTC)
- "forbidden lines" can be of the absorption or emission kind (rules are the same), these lines corresponds to energy transitions which should never occurs (forbidden by the transition rules, generaly because of symmetry reasons), but which, nevertheless, occurs (usually at a very lower intensity) when taking into account all the interactions (causing a small symetry breaking/split of an energy level/...). For example, for infrared lines, collisions between molecules induces small distorsions, which reduce the symmetry, which make possible some transitions otherwise forbidden in the full symmetric case. Need an article of course. -- looxix 17:47 Apr 7, 2003 (UTC)
- OK, now that we've got a forbidden lines article in place, I see what you mean. :) All I knew from the context here was that they weren't emission lines, so I figured they must then be absorption lines. Neat to know about those too, now. -- John Owens 19:04 Apr 7, 2003 (UTC)
Density
Related to density, article says that nebulas have [10 - 10,000,000] particles per cm^3. Could someone explain me to what presure that compares? How many particles per cm3 we have in lab-made vacuum, for instance? saigon_from_europe
"giant H II region"
Am I seeing things or is the "giant H II region" image on the article's top right one of those goatse photoshops?