The Omega Nebula, also known as the Swan Nebula, Checkmark Nebula, and the Horseshoe Nebula catalogued as Messier 17 or M17) is an H II region in the constellation Sagittarius. It was discovered by Philippe Loys de Chéseaux in 1745. Charles Messier catalogued it in 1764. It is located in the rich starfields of the Sagittarius area of the Milky Way.
The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years in diameter. The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter and has a mass of 30,000 solar masses. The total mass of the Omega Nebula is an estimated 800 solar masses.
It is considered one of the brightest and most massive star-forming regions of our galaxy. Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.
--Wikipedia
More:
Messier17 - WikipediaMessier17 - Astropixels.comMessier17 - SEDSI had imaged this previously but have opportunity today to try again with 90% illumination moon below 10 degrees elevation. As processing skills have improved this a much nicer image.
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