Messier 17 – Omega Nebula

Lying amongst the Milky Way star fields over 4000 light years away, M17 is a distinctly reddish nebula due to excitement of hydrogen gas heated up by hundreds of new-born stars embedded in it. It has a white core of hotter gas at its centre, where many of the young stars reside.

The visible nebula is about 15 light years in diameter but the full gas cloud extends way beyond that.

I chose shorter than usual exposures on this occasion, to avoid the risk of trailing stars, as my polar alignment was relatively poor. This image was a 75 minute exposure, composed of 287 x 15.75 sec sub-frames. The lap-top was playing up too, freezing up and dropping quite a few sub-frame images. 

Object Details:

Designation:   Messier 17, NGC 6618.
Constellation:  Sagittarius.
Visual magnitude:  +6.0.
Apparent size:  46′ x 37′.
Diameter:  56.7 light years.
Distance:  4,200 light years.
Altitude during exposure:  65° above NE horizon.

End of blog.
Skip the technical stuff below if you like and leave a comment at the end.

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Exposure:  75 minutes ( 287 x 15.75 sec).
Gain:  440.
Date:  2019-07-08.
Location:  outer suburban.
Conditions:  clear.
Moon: 4 day old crescent.
Sky:  2.04 e/pixel/s.


Image acquisition software:  SharpCap, live stacked.
Image post-processing:  GIMP.
Cropping:   edges only.


Telescope: SkyWatcher Esprit  Type: 120ED triplet refractor
Focal: 840 mm F/7 Mount: SkyWatcher EQ6-R Pro
Camera: ZWO ASI 071 MC Pro Type: CMOS 28.4mm 16 Mpx
Optical aids: Flattener: Y; filter: N Guiding: No
Polar aligning: QHYCCD PoleMaster Polar Error: 12’ 28” (poor)

Geek Log:

[ZWO ASI071MC Pro]
Debayer Preview=On
Output Format=FITS files (*.fits)
Capture Area=4944×3284
Colour Space=RAW16
Hardware Binning=Off
Turbo USB=40
Frame Rate Limit=Maximum
Timestamp Frames=Off
White Bal (B)=60
White Bal (R)=60
Cooler Power=100
Target Temperature=-15
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Anti Dew Heater=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0.154207155477032
#MidTone Point
Display MidTone Point=0.370303618066313
#White Point
Display White Point=0.998046875

Image © Roger Powell


    1. At magnitude +6, I would say there is a good chance, especially as it is very high in the evenings right now, so less atmosphere to pass through. Best to find somewhere to lie horizontal though.


    2. I was out last night with a good view of Saturn and Jupiter and the moon between them. No way was I going to see M-17 sitting just above the nearly full moon. That will have to be another time. 🙂

      Liked by 1 person

        1. I have had a string of good luck lately with clear skies. Starting on the 11th with the Moon right of Jupiter, I’ve had 4 clear ones in a row. Each night I’ve imaged the scene at 9:44pm including Saturn-Jupiter-Moon. Rare skies. I’ve been building a composite with Photoshop showing the Moon’s progression.

          Tonight, I hope to get one more. But, at 9:30:56pm I get a special treat. The ISS will transit the Moon for my location. I will have my eye to the scope for that 1.6 sec. Wish me luck.

          Liked by 1 person

        1. I did get a fifth night of clear skies. You mentioned Saturn next to the Moon like this. It required two exposures due to the large difference in their brightness. Software is very helpful. Let me know if the image doesn’t show for you.

          Liked by 1 person

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