Rob Hawley's Pages Almaden Observatory Main Page

NGC 6888 Crescent Nebula

September - early November 2011

These pages show my work to photograph the Crescent Nebula in narrowband.  I captured Hydrogen, Nitrogen, and Oxygen data from mid September to early November 2011.  This same area was included in my 2012 project.


Click on either of the thumbnails for a full size picture.

NGC 6888 HNO
NGC 6888 area in HNO Palette


Hubble palette
NGC 6888 HON
NGC 6888 in HON Palette

About the Palettes Chosen

Note that all of the images above are the same data.  The images differ on how the three narrowband colors are assigned to Red, Green, and Blue.  The differences in color represent (roughly) differences in the distribution of various elements. Look at the upper right of the area image.  Notice the yellow bands.  These contain a strong return for Hydrogen and Nitrogen. At least for my eyes it is easier to this displayed as yellow. In a CFHT palette (HON) this is displayed as purple. In the Hubble palette (center) these are yellow.  The Hubble palette also converts the purples of CFHT into aquas.



Similarly the vivid edges of the nebula are lost in the NHO image but show clearly in HON.  Note the fringes around the nebula where the O signal is particularly strong.  The crescent has a "hat" of oxygen.  For my eyes this is most easily seen when Oxygen is mapped as green, but if you look closely at the Hubble image you can see an area of blue.

Data Collection and Processing

The image above consists of

# Exposures
34 x 900 sec
31 x 900 sec
32 x 900 sec

The images were processed using PixInsight.  Of special note is each used the new (circa Nov 11) MidScaleMedianTransform and HDRMultiscaleTransform Processes.  These greatly simplified the entire processing sequence. The former both sharpened and eliminated noise. 

About NGC 6888

From Wikipedia

The Crescent Nebula was formed by a Wolf Rayet star WR 136 of type WN6.  Wolf Rayet stars of this type represent the death of massive stars. The characteristic emission lines are formed in the extended and dense high-velocity wind region enveloping the very hot stellar photosphere, which produces a flood of UV radiation that causes fluorescence in the line-forming wind region. This ejection process uncovers in succession, first the nitrogen-rich products of CNO cycle burning of hydrogen  Hence it glows brightly in Nitrogen as shown in my images. .

area dss map

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.