These have been mentioned a couple of times before but I haven't seen any real attempts to produce them in TG. They have been on my "To try", list for a while as I often see them on clear nights around mid-summer. Two things brought them to the top of my list; first
Oshyan posted a link to a web site documenting all kinds of interesting atmospheric phenomena.
http://www.atoptics.co.uk
Second
j meyer used and was kind enough to share a Cloud Density Fractal that looked promising, this was in an experimental thread using vectors passed as density input to a cloud layer:
http://forums.planetside.co.uk/index.php?topic=2648.30Here is the result, the fine structure is not quite there yet but the colouring produced by passing a vector to the density input works well. I added the stars using a clip I downloaded from here, I have not been able to find it again so can't credit its creator. This is where the Comment/Null node discussed elsewhere would have been handy
The first picture is of some Noctilucent Clouds as seen from Glasgow around 01:30 June 30 2007.
C&C welcome.