The Swan Nebula -- M17
Diffuse Nebula
Swan, Omega, Horseshoe, Check Mark, M17, NGC 6618
Integrated Visual Magnitude: 6.0
Apparent Diameter: 46'
Distance: 5000 ly
Actual Diameter: 65 ly

Minimum requirements to view: any telescope under country skies

As bright diffuse nebulae go, it appears that M17 is overshadowed in many people's minds by M42 in Orion and the nearby Lagoon and Trifid. It isn't mentioned at all in Houston's Deep Sky Wonders. Nonetheless, this is a most astonishing object! Somehow over the years I too have never really given this one its due, but it has slowly become my favorite of the summer milky way bright nebulae. To be honest, most of my recent observations have been the result of coming across this magnificent nebula by accident! Each time I do I end up wondering why I don't make a point of looking it up every summer in much the same way I can't seem to get through winter without marveling at M42.

According to Burnham's, the Swan was discovered independently in 1764 by the Swiss astronomer de Cheseaux and Charles Messier. William Herschel described it as "A wonderful extensive nebulosity of the milky kind..."

Any telescope will reveal this nebula as a long streak with a hook at one end, bringing to mind a sort of "check mark." The figure of a Swan can be readily seen with the hook as the head and the long portion its body. A 6-inch or larger telescope at a dark site will reveal many thin dark lanes crisscross the nebula, particularly at the thick end where the neck of the Swan meets the body. 

In my 18-inch f/4.5 the main "check mark" shows considerable fine detail, cut by thin dark lanes, particularly near the blunt end. The OIII filter improves the contrast and brings out faint nebulosity far from the main check, particularly to the east, reaching more than a 44' away from the main body. 

The field in a 6-inch at 50x. North is down and east is right.

Ironically, objects such as M17 sometimes become victims of their own magnificence when it comes to their popularity. Many of us cut our teeth on objects like M17, often with small instruments which didn't reveal all the exquisite detail. As the years go by and  we turn our telescopes toward more challenging objects, they simply become forgotten. Or worse yet, we forget to take the time to really see them when we do look. 

I urge everyone, regardless of the size of your telescope, to go out and spend some quality time with M17, whether you have never seen it, haven't looked in years, or grabbed a quick look just last night. 

Can you see nebulosity in the inner region? How many distinct dark lanes can you make out? How far can you follow the faint surrounding nebulosity?

Millennium Star Atlas Vol III Chart 1367
Sky Atlas 2000 Chart 15
Uranometria 2000 Vol II Chart 294

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