IC 5146

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2021/06/17 and 18

Observation place
My permanent observatory in Longueuil
in white light pollution zone


TelescopeCelestron Edge HD - Diameter 203mm (8``), focal length 2032mm, f / 10
Focal reducerf / 6.3 (63%)
MountCelestron CGEM
Imaging cameraAtik 383 L + monochrome regulated at -20o Celsius
Autoguiding cameraZWO ASI 120MM with one optical splitter
Auto Guidance Accuracy (RMS)June 17 0,99 '' arc RMS (1,98 '' arc total)
June 18 1,96 '' of arc RMS (3,92 '' of arc in total) - Night with wind gusts over 20 km / h
Image typeHa (Ha-OIII-OIII)
ExhibitionHa (13 x 10 'bin 2 × 2), OIII (7 x 10' bin 2 × 2)
Image acquisition softwareMaxim DL
PretreatmentMaxim DL
TreatmentPhotoshop and PixInsight

Object description

Object typeEmission nebula and open cluster "The Cocoon Nebula"
Visual magnitude7,2
Distance 4000 light years
Diameter15 light years
Dimension seen from Earth12 arc minutes 
IC 5146 consists of an emission nebula and an open cluster located approximately 4000 light years from Earth in the constellation Cygnus. Its shape is reminiscent of a cocoon, an envelope that contains insects or a silkworm, hence its common name. It has a diameter of about 15 light years. It is located near the eastern edge of the constellation, near that of the Lizard, right in the Milky Way, one hour in right ascension from the North America nebula. Like other regions of star formation, it is distinguished by a bright red hydrogen gas excited by hot young stars and blue starlight reflected from dust at the edge of a molecular cloud. The bright star near the center of this nebula is only a few hundred thousand years old. It is especially this which illuminates the majority of the nebula and which brings out the very beautiful shades of red color of the nebula.

In a sky of low light pollution, the nebula is visible in a telescope of small diameter. We will then only see the center of the nebula (the cocoon). It takes a large diameter telescope to bring out the faint nebulosities around the nebula.

In my image, which was taken in a site of extreme light pollution (white area), we can see the very beautiful shades of the nebula in the color red. As it is an emission nebula which emits its signal mostly in hydrogen, I used my Hydrogen-Alpha (Ha) filter as a luminance image. At the same time, this filter is very effective in combating the significant light pollution of my observation site. To bring out the very faint blue nebulosities around the nebula, I used an Oxygen III (OIII) filter. The composition of the color image is Ha-OIII-OIII. The Ha filter for the red and the OIII filter for the green and blue layers. This made it possible to bring out the natural colors of the nebula while also bringing out the colors in the stars which approach their natural colors with the traditional RGB filters (red, green and blue).
Richard Beauregard
Sky Astro - CCD
My impression "We cannot be alone in this gigantic universe"