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SH108 Sadr area of Cygnus

May - October 2012
Remastered Nov 2105

small map of mosaic
click for a larger map
My project for the summer of 2012 was the SH108 area around the bright star Sadr in the constellation Cygnus.  Cygnus is well positioned at my location and some DSS images of the area looked interesting.  Last year I imaged the nearby Crescent Nebula.  Originally I started with just the area around Sadr, but then expanded to include a 6 tile mosaic covering the entire area cataloged as Sharpless 108. 

Steve Gottlieb discussed this same area in the September 2012 issue of Sky and Telescope.  His article made me aware of some problems with the cataloging of the area. The multi part IC 1318 is most of SH 108.  What I learned from Steve's article and subsequent emails with him is that the exact labeling of the parts of IC1318 is not locked down. The labeling published by the NGC/IC project and the annotation file supplied with PixInsight differs from the labeling used in Uranometria.  Since Steve used Uranometria I modified the Pixinsight annotation to agree with Steve's article. 

The second problem is that Uranometria labels SH108 as one of the clouds to the SW of Sadr. According to the original paper by Sharpless, SH108 is a 180 arcminute area centered roughly on Sadr. SkyMap Pro (left) shows this as a square of that size which is correct.  Pixinsight uses a 180 arcminute circle which is its form of notation. Uranometria should make clear that SH108 includes almost all of IC 1318.

After seeing the Sky and Telescope article I expanded my original plan of a 6 tiled mosaic into a 9 tile mosaic.  That allowed me to capture the parts of IC 1318 that are not included in SH 108 which matched the picture in Sky and Telescope.  I also added a tile to the SW to capture the clouds around the Crescent and place them in context with the rest of the Sadr nebulosity.

Since this project required a huge amount of data the full mosaic is only H alpha.  I also captured Sulfur and Oxygen data on the central portion (marked in Yellow).

SH108 in H- alpha

Color Slice

Sometimes when you are not satisfied with something it just grates on you. That was the case with the 2012 color version. While the feathery nebula near NGC 6888 looked good, the rest of the nebula was burned out with little detail. Applying the learning from the 2014 Katonah Pixinsight workshop I went back and reprocessed the original data. The version displayed below shows much more detail in SH 108. While the feathery stuff is less prominent, I believe the overall effect is a plus.

Hydrogen dominates the clouds around Sadr. Using the Katonah reprocessing I greatly increased the amount of Sulfur and Oxygen displayed. I also tuned the processing to reveal the subtle structure in SH108.

SH108/IC 1318 in SHO

click for a scrollable image

Hubble palette

"Hat" on Crescent Nebula

As I was processing the images of my original Crescent project last fall I discovered that there is a "hat" of Oxygen visible in the image.  After several attempts I could not get it to show this time.  Its weak signal was buried in the stronger H signal.  Here is the "hat" using just Oxygen.

Crescent In Oxygen

Annotated Images

As mentioned above the exact catalog designations for bright areas of IC 1318 is not nailed down.  Here are the annotations using the designations in Uranometria

SH108 small annotated

click for an annotated scrollable image

Processing Details

This project required a truly massive amount of data.  I started data collection in May right before sunrise and concluded it in October  before my eclipse trip.  The H alpha image consists of 9 mosaic frames.  The central color slice is 3 frames

mosaic layout
click for full size

For the first time I did this entire project bin 2.  I don't fully remember why I did this, but the result was that instead of oversampling seeing problems and then eliminating them in Pixi they became a part of the final image.  While bin 2 is more sensitive, I could have captured the same information bin 1.  Thus on my next project I returned to using bin 1.







(Tile 9 was not used)




I also collected data using Photometric filters to see if I could get correct star colors.  Since I only committed a couple of nights to this my data was less than perfect.  My conclusion was that the extra effort was not worthwhile.

For some reason some of my O images had a high pedestal.  I do not know if this was a transparency issue or some problem with calibration.  I had to use PixelMath to subtract the pedestal before GradientMergeMosaic would correctly process the images.

Copyrights for Photos

Creative Commons License
Except as noted, all work on this site by Robert J. Hawley is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. This permits the non commercial use of the material on this site, either in whole or in part, in other works provided that I am credited for the work.