Messier Objects 20 and 21

The Trifid Nebula, M20 and open cluster M21.

An attempt to improve on my first image, in  black and white, of this pair of objects. This time, the longer exposure of 16 minutes has brought out the  dark blue nebulosity surrounding M20 which is not visible in short exposures.



Exposure: 2 x 8 min  ISO 800.
Date: 2017-08-22
Location: The Oaks, NSW
Sky: semi-dark rural sky, clear.
Processing: Canon DPP, Deep Sky Stacker and GIMP.
Cropping: yes.

Telescope: Skywatcher ED120 refractor, 840mm focal length, f/7 focal ratio.
Mount: SkyWatcher EQ6-R.
Polar aligning: QHYCCD PoleMaster.
Guiding: Orion ShortTube 80 OTA, Orion StarShoot  and PHD2.
Canon EOS 60D. No filter, no flattener.

Object 1:

M20, a glorious nebula in Sagittarius. Known as the Trifid Nebula, its nebulosity is a combination of both emission and reflection nebulae, with dark dust lanes – and it also includes its own local star cluster.
AKA: NGC 6514
Visual magnitude: +6.3
Apparent diameter: 29 x 27 arc-min
Actual diameter: 44 light years
Distance: 5,200 light years

Object 2:

M21, an open star cluster.
AKA: NGC 6531.
Visual magnitude: +5.9
Apparent diameter: 14 arc-min
Actual diameter: 16 light years
Distance: 1,200 light years

Image © R.Powell



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