M17 - the omega or Swan Nebula

Credits: Keith Turnecliff, Long Itchington

M17, also known as the Omega Nebula or Swan Nebula, is one of the largest star-forming regions in the Milky Way galaxy.
The Omega Nebula was discovered in 1745 by the Swiss astronomer Jean-Philippe Loys de Chéseaux. It is located 5,500 light-years from Earth in the constellation Sagittarius. The nebula has an apparent magnitude of 6 and can be seen with a pair of binoculars. M17, which appears near M16 and M18 in the sky, is best viewed on clear nights in August.
M17 contains one of our galaxy’s youngest star clusters, at only 1 million years old. However, many of the young stars in this cluster are impossible to see because of the gas and dust that surrounds them. The powerful radiation from the young stars evaporates and erodes the dense clouds of cold gas in which new stars form. One such pocket of gas is seen at the center of the brightest region of the nebula (near the bottom of this image) and is about 10 times larger than our solar system. Other dense pockets of gas have formed the remarkable dark features jutting inward from the bottom left corner of the image.

Facts about M17 by Keith Turnecliff

The Omega Nebula, also known as the Swan Nebula, Checkmark Nebula, and the Horseshoe Nebula (catalogued as Messier 17 or M17 or 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 star fields 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.
The open cluster NGC 6618 lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars; however, the actual number of stars in the nebula is much higher - up to 800, 100 of spectral type earlier than B9, and 9 of spectral type O, plus over a thousand stars in formation on its outer regions. It is also one of the youngest clusters known, with an age of just 1 million years.