Composite astrophotograph

Copyright Anglo-Australian Observatory.
Photograph by David Malin, Sydney, Australia.

Dusty clouds in the Milky Way galaxy are normally hidden except when they obscure background stars. However, the dark dust of cg-4 is feebly illuminated by light from a nearby star cluster. This light also blows away some of the dusty material in the object's comet-like tail. The red color arises from hydrogen fluorescing in the ultraviolet component of the incident starlight. cg-4's cloud contains enough gas to make close to 60 Sun-like stars. The photograph covers a field of about 22-arc minutes across, or 10 light years at the distance of cg-4.

The original image was captured with the Anglo-Australian telescope (equivalent to a 12.7 m focal length, f/3.3 reflecting objective), on three hypersensitized, monochrome photographic plates with filters that recorded the red, blue, and green bands separately. Each of the three images was photographically amplified to enhance faint detail. The images were then recombined on color negative film to produce a true-color image.