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.

M17 The Omega Nebula (credit:- ESO)

Finder Chart for M17 (credit:- freestarcharts)

Finder Chart for M17 - pdf format (credit:- freestarcharts)

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

Messier17
NGC6618
NameOmega Nebula
Object TypeEmission nebula with open cluster
ConstellationSagittarius
Distance (light-years)5,500
Apparent Mag.+6.0
RA (J2000)18h 20m 47s
DEC (J2000)-16d 10m 18s
Apparent Size (arc mins)20 x 15
Radius (light-years)16
Other NamesCollinder 377

Sky Highlights - July 2017

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for July

Meteor Shower
Southern Delta Aquariids (Aquarids) meteor shower peaks on July 29

Northern Hemisphere
Evening
West:- Mercury (mag. -0.5 to +0.3) (second half of month)
Southwest:- Jupiter (mag. -2.0)
South:- Saturn (mag. +0.2)
Midnight
West:- Jupiter
South:- Saturn
East:- Neptune (mag. +7.8)
Morning
Southwest:- Saturn
South:- Neptune
Southeast:- Uranus (mag. +5.8)
East:- Venus (mag. -4.1)

Southern Hemisphere
Evening
West:- Mercury (second half of month)
Northwest:- Jupiter
East:- Saturn
Midnight
West:- Jupiter
North:- Saturn
East:- Neptune
Morning
West:- Saturn
North:- Neptune
Northeast:- Venus, Uranus

Deep Sky

Small telescopes:-
Messier 13 - M13 - Great Hercules Globular Cluster
Messier 92 - M92 - Globular Cluster
Messier 11 - M11 - The Wild Duck Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 4 - M4 - Globular Cluster
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 16 - M16 - Eagle Nebula (Emission Nebula with Open Cluster)
Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

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