Saturn Nebula

The Saturn Nebula (also known as NGC 7009 or Caldwell 55) is a planetary nebula in the constellation Aquarius. It appears as a greenish-yellowish hue in a small amateur telescope. 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 ejected its layers into space, forming the nebula. The central star is now 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 was one of Struve's nine "Rare Celestial Objects".[4]

Saturn Nebula
Emission nebula
Planetary nebula
Observation data: J2000.0 epoch
Right ascension21h 04m 10.877s[2]
Declination−11° 21′ 48.25″[2]
Distance2000-4000 ly
(See article) ly
Apparent magnitude (V)8.0[3]
Apparent dimensions (V)41″ × 35″[2]
ConstellationAquarius
Physical characteristics
Radius0.2 to 0.4 ly
Absolute magnitude (V)2.5 to 1
Notable features-
DesignationsNGC 7009,[2] Caldwell 55

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.[5] Although the ansae are most prominent in the Saturn Nebula, they are also visible in other planetary nebulae, including NGC 3242, NGC 6543 and NGC 2371-2.

The distance of the Saturn Nebula is not known precisely. 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 solar luminosities and a visual magnitude of 11.5. This strong ultraviolet irradiation from the central star creates 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 towards the Earth.

The nebula is 1 degree west of the star Nu Aquarii. The central portion measures 25″ × 17″, while the outer shell extends to 41″ × 35″. The object is on many "best of" observing lists.[6][7]

Notes
  1. "The Strange Structures of the Saturn Nebula". www.eso.org. Retrieved 27 September 2017.
  2. "NAME Saturn Nebula". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-12-26.
  3. "Messier Online Astronomical Database". Saturn Nebula. Retrieved 2012-08-28.
  4. "NGC 7009, the Saturn Nebula". www.messier.seds.org. Retrieved 2020-12-26.
  5. 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. arXiv:0905.2148. 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.
  6. SAC 110 best NGC object list
  7. RASC's Finest N.G.C. Objects O[http://messier.seds.org/xtra/similar/caldwell.html The Caldwell Catalog (#55)

References

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