Northern Cygnus Mosaic

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About this Image

Subject Northern part of Cygnus constellation
Objects Most notable in this region: NGC7000 North American Nebula, IC5070 Pelican Nebula, SH2-112, SH2-115, LDN 896 Northern Coalsack, IC1318 Gamma Cyg "Butterfly" Nebula, IC1318A "Dolphin" Nebula, B343 "Ghost" Nebula, DWB111 Propeller Nebula, NGC6888 Cresent Nebula, and SH2-104.
Description This is a 12 frame mosaic of the northern portion of the constellation of Cygnus. It covers around a 18x14° swathe of sky. In human terms this is similar in size to the amount of sky covered by the two of your hands held at arms length, with fingers closed and thumbs touching.

The area contains a wealth of objects, starting on the left with the famous North American nebula, its shape remincent of the continent complete with the Gulf of Mexico. Next to this is the Pelican nebula with its characteristic head and long beak. The vast Northern Coal Sack dark nebula separates these bright nebulae from the more easterly Gamma Cygni "Butterfly" nebula, and associated conglomeration of nebulae. Above the Butterfly you can see IC1318A the "Dolphin" Nebula, and above that the Propeller Nebula. The bright nebulae denote areas of recent star birth where the young stars have stimulated their surrounding womb of hydrogen clouds with their energetic UV radiation. The resulting ionization and recombination of the hydrogen atoms cause the clouds to glow, particularly in the hydrogen alpha line picked out by the filter through which this image was captured. The richness of form and structure in this area is generated from a complex interplay of stellar radiation and winds, magnetic fields, and the gravitational collapse of the cold dark nebulae. On the far right of the image is the Cresent Nebula. Embedded within this object is the Wolf-Rayet star WR136. As with all massive stars, it follows a "live fast, die young" policy, and at some point in the next million years or so it will likely go supernova. The Crecent has been formed and sculpted by the star's intense stellar winds & radiation blowing off its own outer envelope and impacting against the local interstellar medium.

The images total resolution after overlapping and combining the individual frames, and cropping, is 8749x6402 or 56 megapixels. This is distilled down from 19hrs of exposure, gathered over a period of eight cloud and moon free nights, generating around 1.75GB of image data. This is quite an investment in available sky time given the usual paucity of cloud and moon free nights in the UK. After this mosaic I decided that I needed to try some less intensive aquisition and processing projects, but somehow got started on a mosaic of the Barnards Loop region of Orion soon thereafter...

The image has been processed to reduce the size of all but the largest stars, enhancing the visibility of dim and dark nebulous areas that fill this region.

Around a month after capturing the data for the mosaic I started processing it, and only at this point discovered an odd object (click for animation) embedded in one nights set of frames. I downloaded an evaluation copy of PinPoint and used this to generate detailed astrometry data for the object. I would recommend PinPoint to anyone interested in trawling for moving objects within their images, and determining the rough direction and movement rate of these objects. I could find no record of a known asteroid or comet around the area at that time. I got excited for a moment thinking I may possibly have come across a new comet! However, experiments with suitable test subjects showed what a 13th magnitude comet (4PFaye) and a 10th magnitude asteroid (5Astrea) really look like with my Ha filtered imaging setup. Here is another animated gif of the unknown object, but this time at an image scale comparable with the Faye and Astrea animated gif images. Follow up attempts to recapture by imaging in the computed target area were fruitless. I doubt I will ever know for certain what it was. The elongated appearance of the object is the hardest aspect to square, and a rocket plume seems a wishful guess. I fear that the true explanation stands a good chance of being something rather more mundane. If you think you can shed some light on this conundrum let me know! Update: June '08, Sung-Nan Lin, an astrophotographer from Taiwan, kindly wrote to me with what looks to be a valid explanation. He uses the same Canon 200mm lens and has noted small ghost reflection arcs from very bright stars in some of his images. While these arcs look a little different from my object, it is likely that the Ha filtering is only allowing the brightest central portion of the arc to be captured. Given the seperations evident in Sung-Nan's example Pleiades images, mag 2.1 Deneb looks to be well placed as the likely source. As the lens position is in theory fixed with regard to the sky, the movement of the ghost arc is still a bit of a mystery - but also evident in Sung-Nan's images. Likely suspect is mount tracking drift.

"The only real mistake is the one from which we learn nothing"

Technical Details

Date(s) Eight nights, 25th August - 26th September 2006
Location Old Dome Observatory, Bourn, Cambridge, UK
Environment 9-19C, mixed conditions, no moon
Optics Canon EF 200mm F/1.8L @F/1.8
Filters Astronomik 13nm Ha
Mount Takahashi EM10
Guiding SBIG STV with efinder
Camera Hutech modified 20D DSLR
Exposure Data gathered: ISO1600 231x300s, over 19hrs total exposure. Good data used: 144x300s, for a total of 12hrs.
Acquisition ImagesPlus
Processing Images calibrated and stacked into frames in ImagesPlus, frames registered together in Registar, final compositing and processing in Photoshop CS.
Notes F/1.8 enables deep images with relatively short exposure times, but does reduce the overall sharpness of the image. If you look at one of the brighter stars at 100% magnification you will see that it is slightly triangular in shape. Due to the amount of data required for a mosaic of this size I erred on the side of quantity over quality, signal over resolution - given the overall resolution of the final combined image this seemed a sensible trade-off. You can read a short description of the lens characteristics here.

SkyMapPro mosaic layout
SkyMap Pro mosaic planning map
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