M-17, An Emission Nebula in Sagittarius
aka The Omega Nebula, (NGC 2068)

M-17 is a bright emission nebula in Sagittarius. It is known as the "Omega Nebula" or the "Swan Nebula". Swiss astronomer Philippe de Cheseaux discovered M-17 in 1746. Charles Messier re-discovered it 1764. Sir William Huggins, in 1866, was the first to study the light of M-17 with the spectroscope; he announced that the cloud was truly a mass of glowing gas, and not merely an unresolved cluster of stars. The Kopernik image above only shows the bright central 8' x 8' arc minute portion of the nebula. One of the largest of the nebulae, M-17 covers about 46 x 46 arc minutes.

P. de Cheseaux: (1746) ''A nebula which has never been discovered: it has a shape quite different from the others: it has the perfect form of a ray or the tail of a comet, 7' long and 2' wide. Its sides are exactly parallel and quite well terminated. The center is whiter than the edges. It makes an angle of 30° with the meridian.'

C. Messier: (June 3rd, 1764) 'A train of light without stars, 5' or 6' in extent, in the shape of a spindle, a little like that in Andromeda's belt (M 31) but the light very faint. In a good sky, seen very well in a 32-foot telescope. Diameter: 5 arc minutes.'

Quote from Burnham's Celestial Handbook:

'For the visual observer, the main feature of M-17 is the long bright comet-like streak across the north edge; on the west end a curved 'hook" gives the whole nebula a resemblance to a ghostly figure "2" with the bright streak forming the base. It requires only the slightest use of the imagination to transform this pattern into the graceful figure of a celestial swan floating in a pool of stars.......The space enclosed by the neck of the swan is evidently an obscuring cloud of some sort, and looks quite dark when compared to the star-strewn sky beyond. Fainter luminous masses extend to the east and north, forming an irregular loop around the whole structure......'

• M-17, NGC 6618
• Magnitude: 6.0
• Constellation: Sagittarius
• RA: 18h 20m 48.0s
• Dec: -16° 11' 00" Epoch 2000
• Size (mins) 46 x 46
• Classification: Emission Nebula.
  

George Normandin, KAS

November 12th, 2007