An Eagle and a Swan in Hydrogen Alpha
An Eagle and a Swan in Hydrogen Alpha
An Eagle and a Swan in Hydrogen Alpha
Strattling the constellations of Sagittarius and Serpens, this widefield image features two beautiful emission nebulae, M16 (the Eagle Nebula) and M17 (the Swan Nebula). M16 is renowned for its beautiful Pillars of Creation that were made famous when the Hubble Space Telescope published its fascinating image of that region. Like M16, M17 is another region of active star formation. Also known as the Omega nebula, the Checkmark Nebula, and the Lobster Nebula, M17 is also the second brightest source of radio energy in the sky.

In this image, I blended 27 hours of Hydrogen Alpha data taken with a wide field 200mm lens along with detail images of M16 (8 hours) and M17 (13 3/4 hours) taken through my Celestron C8 at 1160mm. The detail images were RGB (color) images that I converted to greyscale and then layered into the H-alpha data.

In this image, North is to the left.

Exposure Details
Lens Canon EF 200mm f/2.8L II USM (Base image), Celestron C-8 w/Celestron focal reducer (M16/M17 detail images)
Focal Length 200mm for base image, 1160mm for M16/M17 detail images
Focal Ratio f/3.5 for base image, f/5.8 for M16/M17 detail images
Mount Schaefer GEM - 7 1/2 inch Byers gear
Guiding ONAG On-Axis Guider, Lodestar autoguider, PHD Guiding
Camera Canon 450D - Gary Honis modified (Baader Mod)
Exposure 160 subexposures of 600 sec @ ISO 1600 (26 2/3 hours) using Astronomik 6nm Ha clip filter for base image, 167 subs of 180 seconds @ ISO 1600 (8+ hours) for M16 detail image, 276 subs of 180 seconds each at ISO 1600 (13 3/4 hours) for M17 detail image
Calibration 30 darks, 30 flats, 30 flat darks, 30 bias
Date July 15, July 16, July 30, July 31, 2013 for base image; May 16, 19, and 21, 2012 for M16 detail; June 24, 25, and 26, 2012 for M17 detail
Temperature 58F on 7/15, 7/16, and 7/30, 55F on 7/31
SQM Reading 21.35 (Bortle 4) on 7/15 and 7/16, 21.55 (Bortle 4) on 7/30 21.50 (Bortle 4) on 7/31
Seeing 4/5 on all 4 nights for base image
Location Pine Mountain Club, California
Software Used Images Plus 5.5 for camera control, calibration, stacking, and digital development. Photoshop CS5 used for levels and curves, high pass filter, and unsharp mask. Gradient Xterminator for gradient removal. Registar for registration and stack alignment. Carboni Tools for additional noise reduction and smoothing. Focus Magic for focus restoration.
Notes The very large amount of time I put into capturing Ha data for this field of view seems to have paid off well with very low noise. As it happens, processing this image was surprisingly easy, as the stacked data looked very good with just a digital development stretch. I'm fairly pleased with how the compositing of the detailed RGB images worked, although I probably should have lowered the opacity a bit more to make it blend a little more naturally. Nonetheless, I think it adds some nice detail to the main targets, particularly showing M16's Pillars of Creation rather well.

I had intended to make an HaRGB image with this data and I captured 11 hours of RGB data to do this. However, I haven't found a good method for blending the two sets of data that looks halfway decent to me (in general, I didn't like how my RGB data looks), so I decided for the time being to just settle for a very nice Ha only image.