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This is a completely new image of M20. The previous one can be found here. It had been taken with a similar telescope, but different camera and filters. This image was taken with the CDK 20″, f/6.8, but with narrowband filters (Halpha and OIII), as well as several broadband Blue subframes to be blended with the OIII subframes. This was done in order to be able to take an image of a nebula having both emission (ideal for narrowband filters) and reflection clouds (usually only visible with broadband RGB subframes). The colors were mapped: Ha to Red and 14% Blue (to account for Hbeta), OIII to Green and OIII+broadband Blue to Blue. This method is still being worked out, but looks promising.
This image has been selected as AAPOD (Amateur Astronomy Picture of the Day) on January 14, 2017, see: http://www.aapodx2.com/2017/20170114.html
Additional Information
Object
Name(s): M 20. NGC 6514. The Trifid Nebula
Type: Emission/Reflection Nebula
RA: 18h 02m 35s
Dec: -23º 01’ 54”
Constellation: Sagittarius
Size (arcmin): 29×27
Magnitude: +6.3
Distance: 5,200 ly
Image
Date: 2016-08-28 thru 2016-09-23
Location: iTelescope.net, SSO near Coonabarabran, NSW Australia
Size (arcmin): 37×37
Telescope: Planewave CDK 20” f/6.8
Camera: SBIG STX16803 (4096x4096pix)
Guiding: Astrodon MonsterMOAG off-axis guider
Total exposure: 12h 45m (Ha: 11x30min; OIII: 6x30min; B: 11x15min; RGB (stars): 1.5h)
Processing: CCDStack, Photoshop CC 2015.5