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M17, the Omega (or Swan) Nebula, in hydrogen alpha light.

This is a region of star formation and shines by excited emission, caused by the higher energy radiation of young stars. Unlike in many other emission nebulae, however, these stars are not obvious in optical images, but hidden in the nebula. Star formation is either still active in this nebula, or ceased very recently. A small cluster of about 35 bright but obscured stars seems to be imbedded in the nebulosity.  

This nebula is more massive than the Orion Nebula and is more than 40 light years across. Distance is estimated to be 5000 - 6000 light yrs away.


Image info

Telescope:  Celestron 9.25" Schmidt-Cassegrain at f/6.3

Focus:  Prime focus

Filter:  Astronomik Hydrogen Alpha 13nm FWHM

Mount:  Vixen GPD with Skysensor2000

Camera:  Modified Canon EOS 300D, at ISO800

Guiding:  700mm refractor guidescope, SAC7 camera, autoguided with Guidedog software

Exposure:  Total 117 mins (39 x 180s)

Date:  16th May 2005

Processing:  RAW file conversion, Offset and Dark subtraction, flat fielding, registering and stacking done in IRIS.  Only the Red channel was used.  Curve stretching and a little unsharp masking in Photoshop CS.  Star ovality reduced through making a duplicate layer and offsetting that by half a pixel using the 'darken' blending mode in Photoshop.  Noise reduction in Neat Image.


A humid night in between days of rain - 26 deg C, 95-99% humidity and windless.  Transparency was very good.  Stayed up till 5 am for this! Guiding worked very well indeed - only had to discard 1 out of 40 frames taken.  Total exposure of nearly 2 hrs.


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