Western Veil nebula
|Observation data: J2000.0 epoch|
|Right ascension||20h 45m 38.0s|
|Declination||+30° 42′ 30″|
|Apparent magnitude (V)||7.0|
|Apparent dimensions (V)||3 degrees (diameter)|
|Designations||NGC 6960, 6992, 6995, 6974, and 6979, IC 1340, Cygnus Loop, Cirrus Nebula, Filamentary Nebula, Witch's Broom Nebula (NGC 6960), Caldwell 33/34|
It constitutes the visible portions of the Cygnus Loop, a supernova remnant, many portions of which have acquired their own individual names and catalogue identifiers. The source supernova was a star 20 times more massive than the Sun, and it exploded between 10,000 and 20,000 years ago. The remnants have since expanded to cover an area of the sky roughly 3 degrees in diameter (about 6 times the diameter, and 36 times the area, of the full Moon). While previous distance estimates have ranged from 1200 to 5800 light-years, a recent determination of 2400 light-years is based on direct astrometric measurements. (The distance estimates affect also the estimates of size and age.)
The Hubble Space Telescope captured several images of the nebula. The analysis of the emissions from the nebula indicate the presence of oxygen, sulfur, and hydrogen. The Cygnus Loop is also a strong emitter of radio waves and x-rays.
In modern usage, the names Veil Nebula, Cirrus Nebula, and Filamentary Nebula generally refer to all the visible structure of the remnant, or even to the entire loop itself. The structure is so large that several NGC numbers were assigned to various arcs of the nebula. There are three main visual components:
- The Western Veil (also known as Caldwell 34), consisting of NGC 6960 (the "Witch's Broom", "Finger of God", Lacework Nebula, "Filamentary Nebula") near the foreground star 52 Cygni;
- The Eastern Veil (also known as Caldwell 33), whose brightest area is NGC 6992, trailing off farther south into NGC 6995 (together with NGC 6992 also known as "Network Nebula") and IC 1340; and
- Pickering's Triangle (or Pickering's Triangular Wisp), brightest at the north central edge of the loop, but visible in photographs continuing toward the central area of the loop.
The nebula was discovered on 5 September 1784 by William Herschel. He described the western end of the nebula as "Extended; passes thro' 52 Cygni... near 2 degree in length", and described the eastern end as "Branching nebulosity... The following part divides into several streams uniting again towards the south."
When finely resolved, some parts of the nebula appear to be rope-like filaments. The standard explanation is that the shock waves are so thin, less than one part in 50,000 of the radius, that the shell is visible only when viewed exactly edge-on, giving the shell the appearance of a filament. At the estimated distance of 2400 light-years, the nebula has a radius of 65 light-years (a diameter of 130 light-years). The thickness of each filament is 1/50,000th of the radius, or about 4 billion miles, roughly the distance from Earth to Pluto. Undulations in the surface of the shell lead to multiple filamentary images, which appear to be intertwined.
Even though the nebula has a relatively bright integrated magnitude of 7, it is spread over so large an area that the surface brightness is quite low, so the nebula is notorious among astronomers as being difficult to see. However, an observer can see the nebula clearly in a telescope using an O-III astronomical filter isolating the wavelength of light from doubly ionized oxygen), as almost all light from this nebula is emitted at this wavelength. An 8-inch (200 mm) telescope equipped with an O-III filter shows the delicate lacework apparent in photographs. Smaller telescopes with an O-III filter can show the nebula as well, and some argue that it can be seen without any optical aid except an O-III filter held up to the eye.
The brighter segments of the nebula have the New General Catalogue designations NGC 6960, 6974, 6979, 6992, and 6995. The easiest segment to find is 6960, which runs behind the naked eye star 52 Cygni. NGC 6992/5 are also relatively easy objects on the eastern side of the loop. NGC 6974 and NGC 6979 are visible as knots in an area of nebulosity along the northern rim. Pickering's Triangle is much fainter, and has no NGC number (though 6979 is occasionally used to refer to it). It was discovered photographically in 1904 by Williamina Fleming (after the New General Catalogue was published), but credit went to Edward Charles Pickering, the director of her observatory, as was the custom of the day.
Portion photographed by Hubble Space Telescope
- "NGC 6960". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-01-02.
- Fesen, Robert A.; Weil, Kathryn E.; Cisneros, Ignacio A.; Blair, William P.; Raymond, John C. (2018). "The Cygnus Loop's distance, properties, and environment driven morphology". Monthly Notices of the Royal Astronomical Society. 481 (2): 1786–1798. arXiv:1809.01713. doi:10.1093/mnras/sty2370.
- Nemiroff, R.; Bonnell, J., eds. (1 January 2007). "NGC 6960: The Witch's Broom Nebula". Astronomy Picture of the Day. NASA. Retrieved 2007-01-02.
- Loff, Sarah (24 September 2015). "Veil Nebula Supernova Remnant". NASA. Retrieved 6 September 2018.
- Burnham, Robert (1978). Burnham's Celestial Handbook. New York: Dover. p. 800–811. ISBN 978-0-486-23568-4.
- "Astronomy Picture of the Day: Pickering's Triangle in the Veil". NASA. 17 September 2015. Retrieved 6 September 2018.
- "Cygnus Loop". Encyclopaedia Britannica. Retrieved 6 September 2018.
- "Revisiting the Veil Nebula". spacetelescope.org. Retrieved 2018-01-20.
- Blair, William (September 2015). "The Cygnus Loop/Veil Nebula Hubble Space Telescope" (PDF). hubblesite.org.
- Tirion; Rappaport; Lovi (1991) . Uranometria 2000. 1. Richmond, VA: William–Bell, Inc. p. 120. ISBN 978-0-943396-14-9.
- Tom Trusock, "Small Wonders: Cygnus ...", [section] "The Veil", Cloudy Nights Telescope Reviews
- Frommert, Hartmut. "NGC 6960, 6979, 6992, 6995: Veil Nebula". spider.seds.org.
- "NGC/IC Project". Results for NGC 6974. Retrieved 2010-12-03.
- "NGC/IC Project". Results for NGC 6979. Retrieved 2010-12-03.
- William Blair. "Cygnus Loop HST Photo Release". William Blair Homepage at Johns Hopkins University. Retrieved 2010-11-29.
- "Revisiting the Veil Nebula". Retrieved 1 October 2015.
|Wikimedia Commons has media related to Veil Nebula.|
- Australian Astronomical Observatory – IC 1340, photograph by David Malin
- spacetelescope.com – "Uncovering the Veil Nebula", with several Hubble Space Telescope photos
- APOD (2010-11-19) – Nebulae in the Northern Cross, showing Veil Nebula to scale in Cygnus
- APOD (2010-09-16) – Photo of the entire Veil Nebula
- APOD (2009-12-01) – NGC 6992: Filaments of the Veil Nebula
- APOD (2003-01-18) – Filaments in the Cygnus Loop
- APOD (1999-07-25) – Shockwaves in the Cygnus Loop (and underlying HST photo)
- Bill Blair (Johns Hopkins University) – Cygnus Loop HST Photo Release
- Bill Blair (Johns Hopkins University) – Photo combining optical and X-ray data
- Bill Blair (Johns Hopkins University) – Overview photo of Cygnus Loop and Veil Nebula
- The Veil Nebula on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
- Veil Nebula at Constellation Guide