Trifid Nebula

It’s another clear night sky as I write this – but the Moon is full and it’s not a good time to be taking images. However, only about three or four more days and dark evening skies will be back.

So let’s check the ten day weather forecast:

Oh, crap!  Cloudy skies predicted for the next ten nights in a row! By which time the  b@$#!&* Moon will be almost back again…   😶

I took the above two hour exposure of M20 on 3rd September, it was the third and final image of a field night with Macarthur Astronomical Society,  when the Moon was a four day old crescent and less bothersome. I have already posted the other two images: Crescent Moon and Cat’s Paw Nebula.

This was a two hour exposure of one of the sky’s most charming nebulae. It’s three main lobes, separated by dark lanes radiating from the centre, contribute to its name.

Trifid Dictionery
I wondered what does Trifid mean? This is what revealed.

The Trifid is part of a much larger nebulous complex which also includes M8, the Lagoon Nebula. Some of the complex can be seen as a faint reddish background colour.

The nebula M20 is viewable in binoculars and can be picked out in small telescopes as a fuzzy patch about three quarters of the size of the Moon. 

As I mentioned in my previous post, this image marks my return to image guiding after a period of relying on good polar alignment and shorter exposures. With this object, the guiding worked consistently, considering I was using a new guide camera and had forgotten much of what I had previously learned about PHD2 Guiding

2019-09-03 PHD on M20
2019-09-03 PHD on M20. The graph was consistent for two hours and doesn’t look too bad, even though the Y axis was at it’s greatest option and the exposure level was a bit fast. The main settings were default values.


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Object Details:

Designation:  Messier 20, NGC 6514.
Constellation:  Sagittarius.
Visual magnitude:  +6.3
Apparent size:  29′ x 27′
Diameter:  44 light years.
Distance:  5,200 light years.
Altitude during exposure:  31° above W. horizon.

The following is just technical stuff:


Exposure:  63 x 115.9 sec = 121 min.
Gain: 136.
Date:  2019-09-03.
Location:  semi-dark rural.
Conditions:  clear.
Moon: NM+4 crescent in West.


Image acquisition:  SharpCap.
Method: Live stacked.
Darks: 10x.
Image post-processing:  GIMP.
Cropping:   no.
Sky:   0.27 e/pixel/s .


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: LP Guiding: Yes
Polar aligning: QHYCCD PoleMaster Polar Error: 00’ 28”

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=4 fps
Timestamp Frames=Off
White Bal (B)=50
White Bal (R)=53
Cooler Power=41
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=C:\Users\Roger\Desktop\SharpCap Captures\darks\ZWO ASI071MC Pro\RAW16@4944×3284\118.4s\gain_220\dark_10_frames_-14.8C_2019-09-03T09_45_02.fits
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1


Images © Roger Powell


  1. I like how you describe what you photograph. I can not see the Cat’s Paw’ outline or the Eagle.
    Forgive me for being dense. Fran

    Liked by 1 person

    1. Hello, Fran.

      I take a practical view of these things. Regardless of what people think an astronomical object looks like and no matter what name they have given it, all that really matters to me is what the object acually is.

      However, if you imagine the Cat’s Paw nebula as resembling a PAW PRINT, it may become more apparent. 🤪


      1. Reminds me of being approached by a local officer while watching an occultation of Saturn at something like 2:00 AM. To him it was suspicious activity with a canon. He was easily won over after glimpsing the event. I, was about 15 at the time.


  2. Hi Roger, a small point on PHD – have the exposure time on at least 4 to 5 seconds, this will average out the seeing, that is why your graph is spikey. Try R.A agr at 65, hys at 20 ( again this smooths out guide pulses), R.A minmov 0.15. DEC agr 85, minmov 0.15. Hope this helps. p.s what guide camera are you using.


      1. Thanks Will. I’m using a new ZWO ASI120 for guiding, on an Orion guidescope, after my old Starshoot guide camera carked it.

        I always appreciate suggestions and will use yours as a guide. I guess the settings depend on conditions at the time and everyone has different ideas about how much to deviate from the defaults. I agree with you about exposure time being several seconds, I think I had it much too fast.


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