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Planetary nebula M57, or the Ring Nebula in Lyra.  The central star has thrown off its outer layers in its red giant phase.  The layers expand into space, glowing from the radiation of the hot white-dwarf central star left behind.  The inner blue/green colour is from glowing oxygen and nitrogen, while the outer red is from ionised hydrogen.  Distance is not very well known but is estimated to be just 2300 light yrs.

 

Image info

Telescope:  Skywatcher 8" f/5 Newtonian

Focus:  Prime focus

Camera:  SAC7B, uncooled

Exposure:  60 x 25s 

Date:  27th May 2003

Processing:  The usual YRGB processing, except that the subtraction of a 'banding flat' (see the Advanced Processing page) was done to remove fine banding noise.

Comments

The night had poor transparency, so the quality of the image is something of a surprise.  The new technique to remove the fine banding worked well here and enabled the image to be stretched more and unsharped to show finer detail.  Note the two stars within the ring and one embedded top right within the nebula.

Luminance layering was done to bring out star colours and these show up better than in previous images.

 

   
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