M17 - Omega Nebula
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The Omega Nebula is also known as the Swan, Horseshoe, Lobster, or even Checkmark Nebula. It is one of the brightest and most intriguing emission nebulae visible from Earth. Its catalog designations are Messier 17 (M17) and NGC 6618. Its shape has been interpreted in many different ways by observers over time, which explains the variety of names given to this fascinating object.
Located in the constellation Sagittarius, the nebula lies in one of the richest deep-sky regions of the Milky Way. It is about 5,000 to 6,000 light-years away, in the direction of the Galactic Center. Its true scale is impressive, spanning roughly 15 light-years in diameter and covering an area of 11 by 6 arcminutes in the sky. Under good conditions, it is easily visible through amateur telescopes and even binoculars.
The nebula was first discovered in 1745 by Swiss astronomer Jean-Philippe de Chéseaux. It was later independently observed and cataloged by Charles Messier in 1764, who included it in his famous list of nebulae and star clusters.
Observations
August 10, 2024, around 00:30 AM – Katowice, Poland
urban conditions, very high level of light pollution
The Omega is a classic emission nebula, a glowing cloud of gas, mainly hydrogen, illuminated by the intense ultraviolet radiation from hot, young stars within it (Photo 1). These stars, mostly spectral types O and B, ionize the surrounding gas, causing it to emit the characteristic reddish glow of hydrogen’s Hα line.
Also visible in the image are two smaller nebulae: IC 4706 and IC 4707. The much larger IC 4701 is also present, though it appears faint due to its lower surface brightness. Within it lies the open cluster of young stars NGC 6596.
At the heart of M17 is the young star cluster NGC 6618, which contains several thousand stellar objects. Some are still embedded in dusty clouds and can be observed only in the infrared spectrum. The Omega Nebula remains an active star-forming region, making it a key subject in stellar astrophysics research.
The nebula's structure is highly complex and features luminous hydrogen filaments, dark dust lanes, ionized edges, and stellar wind blown bubbles. It is often compared to the Orion Nebula, though M17 is more massive and compact. Observations from space telescopes such as Hubble and Chandra have revealed stunning details, including shock fronts, protostars, and intricate layers of hot plasma.
Photo 1 Parameters:
- Total exposure time: 80 minutes (stack of 40 RAW frames at 120s each, using an appropriate number of dark, bias, and flat frames)
- Canon EOS 60D
- ISO: 1600
- Achromatic refractor Messier AR-152S (152/760), prime focus exposure
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.
Further readings:
- Desselberger J., Na celowniku Strzelec, Urania – Postępy Astronomii, 2015, 3(777), p. 65
- Povich M. S., Churchwell E., Bieging J. H., Kang M., et al., The Extended Environment of M17: A Star Formation History, Astrophysical Journal, 2009, 696(2), pp. 1278-1306
- Broos P. S., Feigelson E. D., Townsley L. K., Getman K. V., et al., The Young Stellar Population in M17 Revealed by Chandra, Astrophysical Journal Supplement Series, 2007, 169(2), pp. 353-385
Marek Ples