AAO image reference AAT 69a. « Previous || Next »
Top left is NE. Image width is about 44 arc min
Image and text © 2000-2002, Anglo-Australian Observatory, photograph by David Malin.
The spectacular Trifid nebula (Messier 20) is one of the best known in the sky. It is a striking mixture of brilliant red light emitted from excited hydrogen gas and the soft blue glow of a reflection nebula. The blue arises from starlight, scattered by dust particles between the stars. The size of the particles is minute, similar to those of smoke, which also has a bluish hue. However, the scattered light is not a pure blue, and if we see it through a medium that is yellow (i.e. absorbs blue light) some green colouration remains. This effect can be seen in some of the darker parts of the faint reflection nebula that surrounds the Trifid, where partial absorption of light by foreground dust provides a yellow 'filter', producing shades of green. This image has been photographically enhanced using an unsharp mask.
Entry from NGC 2000.0 (R.W. Sinnott, Ed.) © Sky Publishing Corporation, 1988