Diffuse Nebula M17 (NGC 6618), an emission nebula, in Sagittarius.
Also known as Omega, Horseshoe, or Lobster Nebula.

RA 18:20.8 (h:m); DEC -16:11 (deg:m); Distance 5000 light years;
Visual Brightness 6.0 (mag); Apparent Dimension 11.0 (arc min)

The Omega Nebula M17, also called the Swan Nebula, the Horseshoe Nebula, or (especially on the southern hemisphere) the Lobster Nebula, is a region of star formation and shines by excited emission, caused by the higher energy radiation of young stars. Unlike in many other emission nebulae, however, these stars are not obvious in optical images, but hidden in the nebula. Star formation is either still active in this nebula, or ceased very recently. A small cluster of about 35 bright but obscurred stars seems to be imbedded in the nebulosity.

The colour of the Omega Nebula is reddish, with some graduation to pink. This colour comes from the hot hydrogene gas which is excited to shine by the hottest stars which have just formed within the nebula. However, the brightest region is actually of white colour, not overexposed as one might think. This phenomenon is apparently a result of a mixture of emission light from the hottest gas, together with reflections of the bright star light from the dust in this region. The nebula contains a large amount of dark obscuring material, which is obvious in its remarkable features. This matter has been heated by the hidden young stars, and shines brightly in infrared light.

Source and more: SEDS


Wide field image of M16, M17 and M18
August 4, 2009 20:52 - 21:30 UT.
Imaging: 50mm SLR Photolens, Astronomik Ha filter; ATK16IC camera.
Exposures: Ha: 4x300s [1x1] unguided; RGB: not captured: these objects are very low in my skies and my imaging window is only 25 minutes ...

July 24, 2008 22:13 - 22:16 UT.
Imaging: William Optics Zenithstar 80 ED II APO with Meade 3.3 Focal Reducer at f/3 [focal length 240 mm], ATK16IC camera, Astronomik Ha filter.
Exposures: Ha: 1x180s [1x1]; unguided.
Note: only ONE frame, because this object is VERY low for me and M17 hid behind a tree.

July 21, 2006 22:00 - 22:29 UT and July 23, 2006 21:47 - 22:04 UT
On July 23, 2006 I captured the colour image with my LX200 10-inch f/10 telescope with 0.33 Focal Reducer operating at f/4.06 [focal length 1015mm], Vesta Pro-SC3a colour camera, Baader Infra Red Blocking Filter. 46 unguided exposures of 20 seconds. Imaging and post-processing as per my DSO tutorial. I combined this colour image with the b/w image I captured on July 21, 2006; I determined the rotation angle and scale with Astrowave and used Photoshop for layering and colour adjustment

July 21, 2006 22:00 - 22:29 UT
Imaged with LX200 10-inch f/10 telescope with 0.33 Focal Reducer operating at f/4.06 [focal length 1015mm],
Vesta Pro-SC3a b/w RAW camera, Astronomik H-Alpha Filter.
13 autoguided exposures of 90 seconds.

As I live at 52 degrees North, M17 (with DEC -16) is very low for me, as you can see on this picture.
In fact M17 is the lowest object I think I can image from my backyard observatory.
Note: meanwhile M18 is my lowest DEC record holder.

July 29, 2004 21:53 - 21:59 UT
Imaging: TAL-2M 15 cm f/8 @ f/4.6, Baader Infra Red Blocking filter.
Camera: SC3a b/w RAW, 180 exposures of 0.5 seconds. Camera settings [logged with QCamLog]: Brightness 45, Gamma 82, White balance automatic, Gain 90.
Post processing stack: 180 frames.
Full details about the imaging and post processing method on my DSO imaging page, but for this image I also used NeatImage.

July 27, 2004 21:59 UT
Imaging: TAL-2M 15 cm f/8 @ f/4.6
Full details about the imaging and post processing method on my DSO imaging page.