This large emission nebula in Sagittarius has an apparent extension of 90x40 minutes of arc, which is 3 x 1 1/3 the apparent diameter of the full moon, and corresponds to about 140x60 light yrs at its distance of about 5,000 light yrs.

Note the presence of Bok Globules, dark nebulae scattered in the nebula [see detail], which are collapsing proto-stellar clouds with diameters of about 10,000 AU (Astronomical Units).  Some of the more conspicuous globules have been catalogued in Barnard's catalogue of dark nebulae: e.g. long, narrow black B 296 at the south edge of the nebula (lower edge of the detail above).

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 63 mins (21 x 180s)

Date:  20th April 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 just one pixel using the 'darken' blending mode in Photoshop.  Noise reduction in Neat Image.

Comments

New technique to reduce star ovality worked quite well.  Suggested by Erwin van der Velden.  Judicious use (settings much less aggressive than the defaults) of Neat Image was very effective in reducing high frequency noise in the image.