M17, also known as the Omega Nebula, is an emission nebula located in the rich Milky Way star fields of Sagittarius. It's a HII star formation region that shines at magnitude +6.0, placing it at the limit of naked eye visibility. Through binoculars, M17 appears as a diffuse patch of light that's oval shaped. In the same field of view to the south are open cluster M18 (mag. +7.5) and M24, the very large Sagittarius Star Cloud (mag. +4.6).
The Omega Nebula is located 5,500 light-years from Earth. Embedded within it is an open cluster of at least 35 stars that provides the source of the glowing gas. In many similar nebulae such stars are easily visible, but not so in the case of M17. They are hidden deep within the structure and therefore not obvious. In total, there are many hundreds of stars contained inside.
M17 was discovered by Philippe Loys de Chéseaux sometime between 1745-46. Charles Messier independently rediscovered it on June 3, 1764. The nebula covers 20 x 15 arc minutes of apparent sky, which corresponds to an actual diameter of 32 light-years. It's also sometimes referred to as the Swan Nebula, Horseshoe Nebula, Checkmark Nebula or Lobster Nebula.
The object is best seen from southern and equatorial regions during the months of June, July and August.
The Omega Nebula is positioned at the very north of Sagittarius, close to the Serpens Cauda and Scutum constellation boundaries. It's located about 15 degrees north of the teapot asterism of Sagittarius. A couple of degrees south of M18 is M24 with M17 sandwiched between them. The star γ Sct (mag. +4.7) lies 2 degrees northeast of M17 with the Eagle Nebula (M16) located 2.5 degrees west of the star.
M17 is one of the brightest and easily observed emission nebula. It has a high surface brightness and can be seen with the naked eye from a dark site. For most observers this is probably not the case and therefore at least a pair of binoculars will be required. Popular 7x50 or 10x50 models show the omega-shaped bar as a hazy patch of light. When viewed through a 100mm (4-inch) telescope, the nebula appears elongated with subtle differences in brightness visible. A larger 200mm (8-inch) telescope reveals twists, contours and a hook shaped extension at one end. Through even larger scopes, wispy details curving through the structure of the nebula can be seen.
The Omega Nebula is a popular target for astro imagers and a rewarding object regardless of the type of optical instrument is being used. It's one of the best examples of its type in the entire sky.
M17 Data Table
|Object Type||Emission nebula with open cluster|
|Distance (light years)||5,500|
|RA (J2000)||18h 20m 47s|
|DEC (J2000)||-16d 10m 18s|
|Apparent Size (arc mins)||20 x 15|
|Other Names||Collinder 377|