220731 - C27 "Crescent" nebula
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click image to enlarge
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ASTRO:
type=Planetary nebula (pre-supernova) mag=7.4 const=Cygnus dist=5000 ly size=26 ly IMAGE: location=EB Driveway BrtlCls=5 exposure=RGB: DSLR OSC; 113x214s (6.7h), ISO3200 (12bit RGB) OIII: CMOS OSC; 53x300s (4.4h), Gain200 (16bit Lab) EQUIPMENT: camera(s)=Nikon D90 (mod) DSLR - OSC RGB ZWO ASI2600MC-Pro CMOS - OSC Lab (OIII) optics=ES102 w1.0x fltnr, F=714mm, f/7 filter(s)=Radian Triad Ultra Quad NB (RGB) Optolong 6.5nm OIII (Lab) mount=Celestron AVX guiding=Orion 60x240mm, ZWO ASi224MC SOFTWARE: acquisition=Stellarium, APT, PHD2, processing=PixInsight, RCAstro, PhotoshopCC, Lumenzia, APF-R, LrC |
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The Crescent Nebula, also known as Caldwell 27, or C27, and NGC 6888 and Sharpless 105, is an emission nebula located in a dense region of the northern Milky Way, in the constellation Cygnus. This cosmic bubble in space was first 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 slower moving wind ejected by the star when it became a Red Giant around 325,000 years ago.
The result of the collision is a shell and two shock waves, one moving outward and one moving inward. Visible within the nebula, star WR 136 is shedding its outer envelope creating a strong stellar wind, and ejecting the equivalent of our Sun's mass every 10,000 years. The inward moving shock wave heats the outward moving stellar wind to X-ray-emitting temperatures. Burning fuel at a prodigious rate, and near the end of its stellar life, this star is expected go out with a bang in a spectacular supernova explosion.
The Crescent is a rather faint object located about 2 arcdegrees SW of the yellow, supergiant star Sadr (located at the heart of the nebula-rich asterism, "The Northern Cross", or also known as the constellation Cygnus the Swan). It is about 25 light-years across, and located appx 5000 light-years away from Earth.
Ionized oxygen atoms produce a blueish hue in smoother surfaced gas clouds that seem to enshroud the detailed redish folds of the turbulent ionized hydrogen filaments. Due to the nebula's faint surface magnitude, these details are very hard to capture with photographic equipment, making this beautiful object a challenging favorite for amateur astrophotographers. Long integrations with a OIII narrow band filter are needed to bring the blue hues forward into normalized view alongside the red hydrogen elements.
For optical enthusiasts, although the central star shines at magnitude +7.4, the nebula's extremely low surface brightness means a large optic must be used coupled with a nebula filter in order to see it. For most telescopes, a UHC or OIII filter is required. Under favorable viewing conditions a telescope as small as 80mm (with filter) can see its nebulosity only as a faint cloud. Larger telescopes (200mm or more) reveal the Crescent's details more easily. Larger still ground-based Dobsonian telescopes 15 inches and above are ideal for viewing.
The Crescent is best seen from northern latitudes during the months of July, August and September.
The result of the collision is a shell and two shock waves, one moving outward and one moving inward. Visible within the nebula, star WR 136 is shedding its outer envelope creating a strong stellar wind, and ejecting the equivalent of our Sun's mass every 10,000 years. The inward moving shock wave heats the outward moving stellar wind to X-ray-emitting temperatures. Burning fuel at a prodigious rate, and near the end of its stellar life, this star is expected go out with a bang in a spectacular supernova explosion.
The Crescent is a rather faint object located about 2 arcdegrees SW of the yellow, supergiant star Sadr (located at the heart of the nebula-rich asterism, "The Northern Cross", or also known as the constellation Cygnus the Swan). It is about 25 light-years across, and located appx 5000 light-years away from Earth.
Ionized oxygen atoms produce a blueish hue in smoother surfaced gas clouds that seem to enshroud the detailed redish folds of the turbulent ionized hydrogen filaments. Due to the nebula's faint surface magnitude, these details are very hard to capture with photographic equipment, making this beautiful object a challenging favorite for amateur astrophotographers. Long integrations with a OIII narrow band filter are needed to bring the blue hues forward into normalized view alongside the red hydrogen elements.
For optical enthusiasts, although the central star shines at magnitude +7.4, the nebula's extremely low surface brightness means a large optic must be used coupled with a nebula filter in order to see it. For most telescopes, a UHC or OIII filter is required. Under favorable viewing conditions a telescope as small as 80mm (with filter) can see its nebulosity only as a faint cloud. Larger telescopes (200mm or more) reveal the Crescent's details more easily. Larger still ground-based Dobsonian telescopes 15 inches and above are ideal for viewing.
The Crescent is best seen from northern latitudes during the months of July, August and September.