The Omega Nebula (M17 / NGC 6618)
- Tom Shankapotomous
- Oct 3
- 4 min read
About This Series
This project is a long-term effort to document deep space astronomical targets through astrophotography and standard telescopic observation. Each entry combines photography with basic research, aiming to better understand fundamental astronomy while building a catalog of targets under different skies.
The inspiration came during night runs, when I often looked up and wondered what I was seeing. That curiosity evolved into a structured project, blending endurance sport, travel, and science into one ongoing expedition.
I use three methods to build this catalog:
Home Observatory Sessions – images captured at the fixed Shank Gym Observatory (SGO), located on the property near Shank Gym.
Race-Travel Sessions – opportunistic astrophotography from Spartan race and trail race venues across the country and internationally.
Field Expeditions – stand-alone astrophotography trips dedicated solely to observation and imaging.
The ultimate goal is to create a living archive of astrophotography targets, studied under a variety of conditions and light sources.
The long-term goal is to build a catalog of deep-sky targets observed under different skies, conditions, and light-pollution sources — a kind of running logbook that blends science, travel, and endurance sport into one expedition journal.
Acquisition Details SGO-H001
Date: October 2, 2025
Location: Shank Gym Observatory (SGO), (≈ 35.4089° N, –80.5816° W)
Conditions: Mostly clear skies, 64 °F, light cloud cover, estimated Bortle 6 (bright suburban)
Exposure: 1 hour total (30 minutes of stackable subframes at 10s each)
Gear (Imaging): Seestar S50 smart telescope on stock tripod with fluid head, tripod leveler stand, and anti-vibration suppression pads
Gear (Finding/Reference): Seawatch 8″ Dobsonian for initial target acquisition
Backend & Networking: Shank Gym Observatory uses a mesh network for WAN/LAN connectivity between telescope and processing computer; all post-processing completed on a Mac workstation
Target Description
The Omega Nebula, also known as Messier 17 or NGC 6618, is an expansive star-forming region located in the constellation Sagittarius. Positioned approximately 5,000 to 6,000 light-years from Earth, it is one of the brightest and largest emission nebulae in the Milky Way. Even small backyard telescopes can reveal its luminous structure, and its unique shape has led to names like the Swan Nebula, Horseshoe Nebula, and Lobster Nebula. The bright core spans about 15 light-years, while the dimmer outer regions may stretch up to 40 light-years.
At the center of M17 is a dense cluster of young, massive O-type and B-type stars. Their intense ultraviolet radiation ionizes the surrounding hydrogen gas, resulting in the nebula's characteristic red hydrogen-alpha (Hα) glow. Interwoven dark dust lanes and molecular clouds cross the region, serving as reservoirs for ongoing star formation. Astronomers often compare M17 to the Orion Nebula (M42) because both exhibit stellar nurseries with stars at various evolutionary stages. M17 is located in the Sagittarius Arm of our galaxy, one of the Milky Way’s spiral arms.
Multiwavelength observations by NASA — in visible, infrared, and radio — have uncovered thousands of stars embedded in their birth clouds. For amateur observers like myself, the Omega Nebula is a relatively straightforward target during the summer months in the northern hemisphere. For astrophotographers, it provides contrasts: glowing gas, star clusters, and dust structures — a microcosm of galactic processes. This target seemed like an excellent entry point into the first of a series of ongoing fieldwork.
Why It Looks Red
The dominant red hue in your image comes from hydrogen gas. High-energy photons from hot, young stars ionize the hydrogen atoms, ejecting electrons. As those electrons recombine, they emit light at the hydrogen-alpha (Hα) wavelength (656.3 nm). This emission is what gives many star-forming nebulae, including the Orion Nebula, North America Nebula, and Rosette Nebula, their signature reddish glow in astrophotography.
Because our eyes are far less sensitive than cameras, especially in low light, the Hα red is much more vivid in the final image than one might perceive through the eyepiece.
Capture & Processing Notes
This section provides transparency for fellow hobbyists about how the image was created and processed
Data Acquisition: Raw FITS frames saved with “Save Each Frame” enabled in the Seestar app
Transfer: FITS files copied from Seestar to Mac via USB
Stacking: Subframes loaded into ASI Studio → DeepStack as Light frames (no calibration frames used in this session)
Method: Sigma Clipping stacking with star alignment enabled
Output: Master FITS + 16-bit TIFF for processing
Post-Processing:
Auto histogram stretch followed by manual slider adjustments (black/mid levels)
Brightness, contrast, and saturation tuned to highlight nebulosity and star color
Export: JPEG preview exported for sharing; master TIFF archived for reprocessing in Siril/Photoshop
References
European Space Agency. (2015, June 19). Omega Nebula (M17). ESA/Hubble. Retrieved from https://esahubble.org/images/potw1525a/
NASA. (2021, September 7). M17: Omega Nebula. NASA Astronomy Picture of the Day. Retrieved from https://apod.nasa.gov/apod/ap210907.html
O’Dell, C. R. (2001). The Orion Nebula and M17: Two stellar nurseries compared. Astronomy & Astrophysics Review, 39(1), 1–54. doi:10.1007/s001590100010
(Accessible via arXiv: https://arxiv.org/abs/astro-ph/0109487)
Royal Astronomical Society of Canada. (2022). Messier 17 – The Omega Nebula. RASC Observer’s Handbook Online. Retrieved from https://rasc.ca/m17-omega-nebula
Closing Note
This was the first “mission report” from SGO under suburban Bortle 6 skies. The Omega Nebula is a forgiving target — bright enough to punch through local light pollution, but detailed enough to reward longer integration. Future sessions will experiment with calibration frames and more advanced processing workflows.
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