Trifid Nebula

Messier 20, NGC 6514, Barnard 85

Classification:Emission, reflection and dark nebulae (B85).
Magnitude: +6.3.
Apparent size:29′ x 27′ (about Moon size).
Diameter:44 light years.
Distance:5,200 light years.
Image date:7th September 2020.
Exposure:121 x 90 sec = 181 minutes.
Field of View:47.7 x 31.7 arcmin. Up is 173 degrees E of N°

The Trifid Nebula is another favourite object for amateur astronomers. I last imaged it only last year but since I added the 2X Televue Powermate I wanted to see what it looked like a bit closer up.

M20 is unusual because it contains three different classes of nebulosity:

  • The large red emission nebula is excited by the extreme ultra-violet radiation from the hot new stars near its centre.
  • The blue reflection nebula is illuminated simply by the reflected light of nearby stars. It is prominent in the north (down) but actually faintly surrounds the entire emission complex.
  • The black lanes are a series of dark absorpsion nebula in front of the emission nebula.

Three for the price of one!

Here is last year’s 1X image, for reference:

2019-09-03 M20 Trifid Neb Stack_63frames_7303s 2

The large star at the centre of the emission nebula is listed as HD 164492, a 7th magnitude double star system O type star with a 10th magnitude companion. Together with other hot nearby stars they form a multiple system of at least six stars which formed inside the nebula and are responsible for ionising the nebula.

The bright star which appears in the middle of the blue reflection nebula is 7th magnitude HD164514, an A type giant. At a distance of only 384 light years it is a foreground star, not a physical component of the Trifid complex.

No filter was employed in the main feature photo, I’ve been waiting nearly a month for a new dual-pass filter from China. I hope the current tensions between Australia and China will not delay delivery…..🥱

This is my second time out with EQMOD installed, which has greatly improved the accuracy of navigation to my targets. It integrates with the planetarium software Cartes du Ciel (left & mostly hidden) to provide greater target alignment accuracy. It is successfully operated using a game-pad controller but gets annoying if I accidentally hit the ‘vibrate’ button.

Software screenshot (left to right): Cartes du Ciel (star map), SharpCap (Imaging management) and EQMOD (navigation).

Telescope Information
SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Field flattener; 2x Powermate
SkyWatcher EQ6-R Pro mount; No filter; ZWO ASI120 guide camera.
Camera: ZWO ASI 071 MC Pro (CMOS 28.4mm 16 Mpx).
Software: EQMOD, Cartes du Ciel, PHD2, SharpCap, Gimp.
Observatory location: 34° South.

See annotated image at

The Seven Best Southern Sky Objects


    1. Thanks, Dave. The sky readings were so much better with a filter but I destroyed the thread on my first one, so have been operating without one for a few weeks.

      Yes the controls are improved with EQMOD. Better accuracy. I’m looking at plate-solving as my next improvement.



  1. 35+ years ago I was behind an elementary school near my home looking at M20 through a Celestron 8″. I was plugged into an outlet and enjoying the nice dark site. Views were excellent. I noticed a person walking their dog across the school yard in the dark but didn’t think much of it. About 10 minutes later a policeman came around the corner toward me with a very bright light shined into my eyes. There went the night vision adaptation. He asked some questions and let me be.

    Liked by 2 people

    1. Some of our members use laser pointers, which could attract attention to our activities and I’ve often wondered if one day the police will turn up with headlamps blazing but surprisingly it’s never happened.

      We did once get a visit from some hoons in a car. We heard them doing wheelies on approach. Then they entered our field, which is some distance from the road. They got spooked when they saw us in the middle of the field in the dark – and their departure was even faster than their arrival!

      Liked by 1 person

    1. I do occasionally get satellite trails in my images. Starlink hasn’t affected me yet but inevitably it will affect how we all see the night sky. 🙁

      The astronomy world is pretty upset about the prospects of a rampant billionaire desecrating the night sky with tens of thousands of unnecessary satellites to provide himself with an even bigger income stream.

      There are no rules covering what private enterprise can do in outer space and no doubt other organisations will want to launch similar systems to compete and set up their own mega space networks.


  2. Wow, that is such a vivid explosion of color! It’s interesting comparing the new image with the past one. Does the nebula rotate? The lines of the absorpsion nebula look like they’re at different angles.

    Liked by 1 person

    1. Good question but no, this type of object does not have any significant angular momentum. It’s just the effect of a different camera angle.
      Most likely the nebula is expanding in diameter, although the effect would be barely noticeable over a human lifetime.

      Liked by 1 person

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