NGC 6888 (Sh2-105, Crescent Nebula) in Cygnus




© Velimir Popov & Emil Ivanov 2020
Size: 2000 px
NGC 6888 (also known as Caldwell 27, Sharpless 105 or The Crescent Nebula) is an emission nebula in the constellation Cygnus, about 5000 light-years away from Earth. It was discovered by William Herschel in 1792. It is formed by the fast stellar wind from the Wolf-Rayet star WR 136 (HD 192163) colliding with and energizing the slower moving wind ejected by the star when it became a red giant some 250,000 to 400,000 years ago. The result of the collision is a shell and two shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray-emitting temperatures. It is a rather faint object located about 2 degrees SW of Sadr. For most telescopes it requires OIII filter to be photographed. For this image were needed four hours (240 minutes) of exposure time in OIII filter.

Image details:


Center of field RA 20:12:08 (h:m:s)
Center of field DE +38:21:12 (deg:m:s)
Size 46.3 x 33.9 (arcmin)
Pixel scale: 1.39 (arcsec/pixel)
Orientation: Up is 90.2 degrees E of N
Charts and image details obtained from
Optic(s): ASA 12" Astrograph @ f/3.6 (Newton)
Mount: ASA DDM85 Standard
Camera: SBIG STL 11000 M
Filters: Luminance, Red, Green, Blue, Astronomik filters
Dates/Times: July - August .2011
Location: IRIDA Observatory, BG, longitude: E 24 44' 18", latitude: N 41 41' 42"
Exp. Details: R:3x10 min, G:3x10 min, B:3x10 min; Ha:8x30; Oiii:8x30. Bin 1 Total exp.time: 570min 9:30 hrs
More details: Dark and flat frames reduction
Processing: PixInsight / PS
Copyright: Velimir Popov and Emil Ivanov 2020. All Rights Reserved
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