Trifid Nebula and M21

Image information:

Date: 06/19/2022
Equipment: Altair Hypercam 533C colour camera through APM/LZOS 105/650 APO telescope using IDAS LPS filter on Losmandy GM8 mount. The telescope was working at f6.2 with Astro-Tech 2" field flattener.
Image type: OSC
Exposure time: 80X3min, gain 250 (0.8e/ADU).
Comment: M20 is a rather difficult object for me, since it never rises more than 20 degrees above the horizon at my site.

Object information:

Object designations:

  • M20, NGC6514, Trifid Nebula, Barnard 85 (dark nebula)
  • M21, NGC 6531, Webb's Cross
Object type:
  • M20 - diffuse emission and reflection nebula, dark absorption nebula
  • M21 - open cluster
Object size:
  • M20 - 28'
  • M21 - 14'
Constellation: Sagittarius

M20 is an interesting object showcasing three main types of astronomical nebulae. Red portion of M20 is emission nebula glowing in the light of excited hydrogen atoms. Hydrogen is excited by the cluster of hot young stars in the center of the nebula. Blue portion of the nebula is reflection nebula, actually interstellar dust reflecting starlight. M20 owe its name, Trifid nebula, to dark absorption nebula that divides it into three main lobes. Dark nebulae are dense clouds of interstellar dust obscuring the light of objects behind them. The distance of the Trifid nebula is not precisely determined, it is estimated to some 5000 ly

M21 is a young and still quite dense cluster. It is some 4.6 million years old with its 60+ stars packed in diameter of 16 ly. It is some 4250 ly distant from us.

Related images:

List of related images:

M20 Trifid Nebula , LRGB, ST2000XM through WO ZS105ED telescope