Omega Nebula

Omega Nebula
Omega Nebula from Hubble Space Telescope Credit: NASA/ESA/STScI
Observation data: J2000 epoch
Type	Emission
Right ascension	18h 20m 26s[1]
Declination	−16° 10′ 36″[1]
Distance	5,000-6,000 ly
Apparent magnitude (V)	+6.0[1]
Apparent dimensions (V)	11 arcmins
Constellation	Sagittarius
Physical characteristics
Radius	-
Absolute magnitude (V)	-
Notable features	-
Other designations	M17, NGC 6618, Swan Nebula[1], Sharpless 45, RCW 160, Gum 81
See also: Diffuse nebula, Lists of nebulae

The Omega Nebula, also known as the Swan 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. The total mass of the Omega Nebula is an estimated 800 solar masses.
A cluster of 35 stars lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars.

Three-colour composite image of the Omega Nebula (Messier 17, or NGC 6618). Credit ESO

A colour-coded composite image of a sky field in the south-western part of the galactic star-forming region Messier 17. Credit: ESO