Messier 16 (M16) - The Eagle Nebula
September 8 and October 3, 2023

Messier 16 (M16), the famous Eagle Nebula, is a star-forming nebula best known for “The Pillars of Creation” region, three large pillars of interstellar gas, famously photographed by the Hubble Telescope in 1995.  The name Eagle comes from the nebula’s shape, which is said to resemble an eagle with outstretched wings.  The Eagle Nebula can be found where the constellations Scutum (the Shield), Serpens (the Snake), and Sagittarius (the Centaur) come together, in the Sagittarius Arm of the Milky Way Galaxy, the next inner spiral arm from our own.  Lying about 5,700 light-years distant from Earth, the photons of light that were collected to bring you these images left the Eagle Nebula 700 years before the construction of Stonehenge began.  It is not visible to the naked eye, with an apparent magnitude of 6.4. M16 subtends about 30-40 arc minutes of the sky, roughly the angular diameter of a full Moon.

Surrounding the open star cluster is a diffuse emission nebula (an H II region), containing vast regions of active star formation. One such region is the aforementioned Pillars of Creation in the central part of the nebula and the Stellar Spire, located just to the left of the pillar structure.  The darker areas of the Pillars of Creation (and other similar areas) are composed of gas and dust and are protostars, stars in development, also known as Bok Globules.  The largest of the three Pillars of Creation is approximately 4 light years high – the distance from Earth to our nearest stellar neighbor, Alpha Centauri. The Stellar Spire, a large tower of gas that appears to be coming off the region of nebulosity, is about 9.5 light years high, or roughly twice the distance from the Sun to Alpha Centauri.This image of M16 has a total exposure time of 3 hours and 37.5 minutes.  The frames used for stacking in Astro Pixel Processor (APP) were gathered during imaging sessions on September 8 and October 3, 2023.  The additional 90 minutes of exposure time from October 3rd brought out the surrounding nebulosity. With the current weather, look angle, and surrounding obstructions, I doubt I will get any more time on M16 this year.  Next Spring and Summer, I will be looking to add another 4+ hours under my Bortle 7 skies to really bring out the glowing dust clouds surrounding M16. 

My initial stacking and post-processing attempt on this combined data set went well, but I noticed some minor star distortion towards the edges that I had not noticed in the past. I was either not as well focused as I thought, or I may need another thin shim to achieve proper back focus.  Regardless, I was not happy with the result, as it could have been better.  To reduce the effects of marginal frames, I culled additional subs based on APP’s Quality score, Star Shape (> 70%), and max FWHM (<3.70).  These better matched the FWHM star shape numbers obtained during image focus FWHM (2.7-3.1).  I also integrated the subs using APPs Local Normalization Correction, performing the minimal 1st degree LNC with one LNC iteration.  Cleaner data and using Local Normalization Correction appeared to clear up the coma-looking artifacts.  It is not perfect, but one has to pixel peep to find it now. APP’s Calibrate Star Colors function removed the heavy red/magenta tint of my earlier efforts, making the colors of Eagle Nebula appear more natural. 

The resulting APP-stacked image was further processed using APP’s Star Reducer tool to reduce the size and intensity of the surrounding stars (50% Size, 50% Intensity).  StarNet++V2 produced a starless, nebula-only, image.  This allowed me to enhance only the nebulosity, without affecting any surrounding stars.  Both the starless, nebula-only image, and the star reduced image were given some degree of post-processing in PhotoShop, and included the use of Russel Croman’s Noise eXterminator for PhotoShop program.  The final “star reduced” and “nebula only” images were recombined into a single image, showing both the Eagle Nebula and surrounding stars.  This final image was further polished in LightRoom, and included a touch of Topaz Labs Sharpen AI to give it a bit more “pop.”

Exposure Information:  ISO 800, 130 frames and 217.5 mins, or 3 hrs 37.5 min total integration time·       

September 8, 2023 Lights & Master Darks:  ISO 800, 85x 90 sec subs and 1 Master Dark; 127.5 mins total time·       
October 3, 2023 Lights & Master Darks:  ISO 800, 45x 120 sec subs and 3 Master Darks; 90 mins total time·       
Common to Both Data Sets:  3 Master Bias and 1 Bad Pixel Map 

Equipment and Software·       
AstroTech AT70ED with ATR8 0.8x FF/Reducer and IDAS LPS-D3 filter imaged by an Ha-modified Canon T3i·       
Mount: EQM-35Pro with ASI 120-MM-mini with ZWO 30mm f/4 guide scope and camera controlled by PHD2·       
Session Control via BeeLink mini-PC running EQASCOM, Carte du Ciel, ASTAP, BYEOS, and Polemaster with remote control via Windows Remote Desktop from a laptop.[b] [/b]

Guiding Comments:  Guiding with my EQM-35Pro has been problematic as of late, excessive backlash is the root cause, I believe.  Guiding on October 3rd was not great at 1.36 arc-sec total error, but that represents only about ¼ of a pixel on my guide camera.