M16 The Eagle Nebula

Emission Nebula in Serpens

Uploaded 8/27/06

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The seeing held steady for this rendition of the famous Eagle Nebula, shot during a one day lull in the constant supply of hard rains and thick clouds that fill our skies during the monsoon season here in Arizona. With only an hour of exposure time before the heavy dew shut me down, I paid critical attention to collimation and focus to get the best images possible. And this is the result of that effort.

One of the brightest nebulosities in the Summer sky, M16 is the star cluster you see just above center, and at a bright 6th magnitude, contains nearly 600 known cluster members in an area of 6 arcminutes. The large red hydrogen nebulosity here is actually IC4703, traditionally listed at half a degree in size. This field which is just over half a degree wide reveals that the nebula is considerably larger than the cataloged size. The colors of the stars in this image are nearly all yellows and reds. The lack of blues emphisizes the fact that there is a huge amount of obscuring dust in this part of the sky, and shorter wavelenths are severely attenuated.

Photographically, this nebula provides some unique challenges. The central dark nebulosity, known as the "Star Queen" or more recently as Hubbles "Pillars of Creation" are low contrast against the bright nebula. Applying the normal gamma curve function to bring up the dim areas of nebulosity results in lowering the contrast even more. Here, I settled on a compromise between the visibility of the Star Queen and revealing the outermost nebulous wisps.

Processing notes.

30 minutes of unbinned RGB data was supplemented by another 30 minutes of 6nm Halpha images. The goal in combining the Hydrogen data into the RGB data was to keep accurate G2V stars, and keep the rosy pink nebulosity as close as possible to the original RGB coloration. The red channel was removed from the processed RGB image, and combined with "lighten" with the Ha data at 100 percent. Next, to capture the Hbeta data that is also present in the original RGB data, we combined 10% of the Ha data into the blue channel with lighten. By recombining the three channels as a new RGB image, we were able to keep the stars at their proper brightness and colors, while tastefully importing additional hydrogen data into the image. A final note on adding the Ha data into the blue - add only as much as it takes to obtain the same shade of pink in the original RGB image, here about 10%. NO noise reduction was used on this image.

Instrument: 12.5" f/5 Home made Newtonian Platform: Astrophysics 1200 QMD CCD Camera: SBIG 10XME NABG with Enhanced Water Cooling Guider: SBIG ST4 Exposure: Ha+RGB = 30:10:10:10 RGB Combine Ratio: 1: 1.05: 1.11 Filters: AstroDon RGB Tricolor Location: Payson, Arizona Elevation: 5150 ft. Sky: Seeing FWHM = 5 arcsec (Maxim DL - 10min subframe), Transparency 8/10 Outside Temperature: 60 F CCD Temperature: -30 C Processing Tools: Maxim DL, Gralaks Sigma, Photoshop, PixInsight, Starizona Debloomer. HOME GALAXIES EMISSION NEBS REFLECTION NEBS COMETS GLOBULARS OPEN CLUST PLANETARIES LINKS


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