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Open Cluster M16 and the Eagle Nebula, in hydrogen alpha light.

Lying some 7,000 light years distant in the constellation Serpens, close to the borders to Scutum and Sagittarius, and in the next inner spiral arm of the Milky Way galaxy from us (the Sagittarius or Sagittarius-Carina Arm) a great cloud of interstellar gas and dust has entered a vivid process of star formation.  Open star cluster M16 has formed from this great gaseous and dusty cloud, the diffuse Eagle Nebula IC 4703, which is now caused to shine by emission light, excited by the high-energy radiation of its massive hot, young stars.  It is actually still in the process of forming new stars, this formation taking place near the dark "elephant trunks".

The stars in the cluster are only about 5.5 million years old with star formation still active in the Eagle Nebula; this results in the presence of very hot young stars of spectral type O6.  The brightest star of M16 is of visual magnitude 8.24.  The nebula extends to a diameter of over 30', corresponding to a linear size of about 70x55 light years.


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 42 mins (14 x 180s)

Date:  17th 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 1.5 pixels 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.  I was surprised that the image is acceptable though a little noisy, given that exposure time was less than ideal, and that the corrector plate started to dew up towards the end of the imaging session.  The guidescope dewed up as well, making guiding inaccurate.


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