The 'reddened' nebulosity of NGC 6357
AAO image reference UKS 12.    « Previous || Next »

The 'reddened' nebulosity of NGC 6357
Top left is NE. Image width is about 75 arc min
Image and text © 1979-2010, Australian Astronomical Observatory
Photograph from UK Schmidt plates by David Malin.

The star-forming nebulae NGC 6334 (UKS 11) and NGC 6357 show no evidence of a blue component in their colour - indeed, the blue-light plate used in these 3-colour pictures had no nebulous image at all - nor is there any obvious sign of the bright blue stars normally found in these objects. They are excellent examples of the phenomenon known as 'interstellar reddening', the selective removal of blue light by minute particles of dust in the line of sight. This accounts for both the ruddy hue and apparent absence of blue stars. The hot stars are present but only some of the red part of their light is seen so they are not conspicuous.

These nebulae are quite nearby (5500 light years) in the direction of Scorpius, but located close to the Galactic plane and buried in the dust of the Milky Way. Careful measurement of the colour of stars associated with the nebulae indicate that they are dimmed by a factor of about 10 in the green part of the spectrum, much more in the blue, but relatively little at red wavelengths. The scattering of bright stars seen here are in the foreground so are relatively unaffected by interstellar reddening. Some care has been taken to ensure that these images are as close to true-colour as possible.

Related images
UKS 10.  NGC 6334 and 6357 in the Galactic plane
UKS 11.  NGC 6334
Constellation of Scorpius (external site)

For details of object position and photographic exposure, search technical table by UKS reference number.

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Updated by David Malin, 2010, July 25