The central area of M16 - the Eagle nebula, and the famous Hubble's "pillars of creation" . One of the most imaged areas in the Northern summer sky, M16 is an active area of star formation. The pillars are clouds of hydrogen and dust, serving as stellar incubators. According to observations from the Spitzer IR telescope, a supernova remnant exploded and disturbed the pillars area 8-9000 years ago. That is about how far the object is in light-years, but the supernova shockwave travelling through it, didn't disturb the pillars for another few thousand years. This change will not reflect here on earth for another millenium, according to observations. So here you are witnessing the ancient light of the nebula as it appeared 9000 years ago. Mind blowing, isn't it?
There is a story behind every image, and this one's no different. The Ha data for this image was collected exactly a year ago as a test exposure for the then newly acquired Astrotech 12'' RC telescope. I was astounded by the amount of detail shown in the pillars. While I liked the image, I never got the chance to collect the color information, because the target was out of range, low in the west by early fall. I then decided to use the color from an older image taken with my older 8'' Vixen cassegrain. I was never happy with the results, as the red channel is much stronger than the green and blue and tends to overtake the image, while diminishing contrast.
I made multiple attempts to color process the image during the year, always giving up in the end.
Fast forward to today, and I have learned that making a synthetic luminance channel out of the color data by adding up all the channels. I then create an LRGB image only from the color data, before adding it to the luminance or Ha. This is a technique I employ in almost all of my new images now, which gives them a better color boost. This particular view still took a lot of trial and error with the color balance. I found this interpretation appealing for a few reasons. First, the object brightens to a bluer hue towards the center, and has a more red/green (yellow) appearance in the fainter areas. So in a way it's at least a bit true to the natural color. Secondly, this color palette dramatically improved the contrast in the pillars and darker areas, while maintaining a beautiful color combination. What really helped was boosting the "b" channel in the Lab color space, which brought out the yellows in the stars, as well as the blues in the central region. Finally, during the LRGB combine, I backed off the lightness channel about 25% to avoid getting the salmon looking effect typical of a much stronger Ha signal. The star layer was copied back over, as stars had been adversely affected after the combine. Technical card:
Messer 16 - Eagle nebula in Serpens
Imaging telescope: AT12 RC astrograph f/8 (Ha), Vixen VC200L f/9 (color) Imaging camera: QHY9M CCD Filters: Orion 2'' LRGB, 2'' Baader 7nm Ha Mount: AP900 GTO Guider: Meade DSI Pro II, Robofocus Software: CCD Commander, Maxim DL, Photoshop CC 2014, Pixinsight 1.8
Date: Ha: July 20, 2016 RGB: Jun 24, 2015 Exposure: Ha: 12x1200'' bin1, RGB: 7X600'' each bin2 Total integration 7.5 hours Location: Asteria remote observatory, Hocking Hills, Ohio, US
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