M17 Ha

The Omega Nebula, also known as the Swan Nebula, Checkmark Nebula, Lobster Nebula, and the Horseshoe Nebula (catalogued as Messier 17 or M17 and as NGC 6618) 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)

This represents 3.5 hours of data taken in 10 minute subs. It is monochrome as it was all taken through a Hydrogen alpha filter which allows only a very narrow section of the spectrum through to the camera. If I added RGB data, this would look quite red. The H alpha light imaged here represents the energy released as elections hat have been boosted to high energy levels by radiation from new hot stars formed in the nebula give up that energy as they drop to a lower orbit. This energy has a very specific wavelength - right in the middle of the filter's bandpass.