Saturn Nebula


Saturn Nebula
Saturn Nebula
NGC 7009 Hubble.jpg
NGC 7009 by Hubble Space Telescope
Observation data
(Epoch J2000.0)
Right ascension 21h 04m 10.877s[1]
Declination -11° 21′ 48.25″[1]
Distance 2000-4000 ly
(See article)
Apparent magnitude (V) 12.8[1]
Apparent dimensions (V) 41″ × 35″[1]
Constellation Aquarius
Physical characteristics
Radius 0.2 to 0.4 ly
Absolute magnitude (V) 2.5 to 1
Notable features -
Other designations NGC 7009,[1] Caldwell 55
See also: Planetary nebula, Lists of nebulae

The Saturn Nebula (also known as NGC 7009 or Caldwell 55) is a planetary nebula in the constellation Aquarius. It was discovered by William Herschel on September 7, 1782, using a telescope of his own design in the garden at his home in Datchet, England, and was one of his earliest discoveries in his sky survey. The nebula was originally a low-mass star that transformed into a bright white dwarf star of apparent magnitude 11.5. The Saturn Nebula gets its name from its superficial resemblance to the planet Saturn with its rings nearly edge-on to the observer. It was so named by Lord Rosse in the 1840s, when telescopes had improved to the point that its Saturn-like shape could be discerned. William Henry Smyth said that the Saturn Nebula is one of Struve's nine "Rare Celestial Objects."

The Saturn Nebula is a complex planetary nebula and contains many morphological and kinematic sub-systems in three dimensions. It includes a halo, jet-like streams, multiple shells, ansae ("handles"), and small-scale filaments and knots. The ansae are expanding non-radially from the central star.[2]

The distance of the Saturn Nebula is not known precisely because no reference stars have been detected in its neighborhood that could be used to accurately gauge it. Therefore any distance given is somewhat suspect. Sabbadin et al. 2004 estimates the distance to be 5,200 light-years (1.6 kpc). In 1963 O'Dell estimated it to be 3,900 light-years (1.2 kpc), which gives an approximate diameter of 0.5 light years for the object as a whole.

The central star, a very hot bluish dwarf with a temperature of 55,000 K, from which the nebula is believed to originate, has an absolute magnitude of +1.5, which equates to a luminosity of about 20 Suns and a visual magnitude of 11.5. This strong ultraviolet irradiation from the central star is believed to create the characteristic fluorescent green tint of the nebula via the radiation of doubly ionized oxygen. The object overall has a visual magnitude of 8 and a radial velocity of 28 miles per second in approach.

The nebula can be spotted 1 degree west of the star Nu Aquarii. The central portion measures 25″ 17″, while the outer shell extends to 41″ × 35″. It is a beautiful object with a high surface brightness.

The object is on many "best of" observing lists, including: SAC 110 best NGC object list, RASC's Finest N.G.C. Objects Objects, and The Caldwell Catalog (#55).

Notes

  1. ^ a b c d e "SIMBAD Astronomical Database". Results for Saturn Nebula. http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Saturn+Nebula. Retrieved 2006-12-26. 
  2. ^ Steffen, W.; Espíndola, M.; Martínez, S.; Koning, N. (October 2009). "The 3D velocity structure of the planetary nebula NGC 7009". Revista Mexicana de Astronomía y Astrofísica 45: 143–54. Bibcode 2009RMxAA..45..143S. "NGC 7009 is a planetary nebula with several morphological and kinematical sub-systems with multiple shells, a halo, jet-like streams, ansae and small-scale filaments and knots." 

References

External links

Coordinates: Sky map 21h 04m 10.877s, −11° 21′ 48.25″


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