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Helene

 
Dictionary: He·lene   (hə-lēn') pronunciation
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n.
A satellite of Saturn.

[Greek Helenē, name of Amazon that battled Achilles.]


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Columbia Encyclopedia: Helene
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Helene (həlēn', hĕl'ənə), in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn XII (or S12), Helene is an irregularly shaped (nonspherical) body measuring about 22 mi (36 km) by 20 mi (32 km) by 18 mi (30 km); it orbits Saturn at a mean distance of 234,500 mi (377,400 km) and has an orbital period of 2.7369 earth days-the rotational period is unknown but is assumed to be the same as the orbital period. It was discovered by French astronomers P. Laques and J. Lecacheaux in 1980 during ground-based observations of Saturn. Another moon, Dione, is co-orbital with Helene; that is, Helene orbits Saturn at the same distance as Dione but precedes Dione by about 60°. Before the present name was adopted, the moon was referred to as "Dione-B" and "Electra."

Wikipedia: Helene (moon)
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Helene
File:Cassini Helene N00086698 CL.jpg.jpg
Discovery
Discovered by Laques and
Lecacheux
Discovery date March 1, 1980
Semi-major axis 377,396 km
Eccentricity 0.0022
Orbital period 2.736915 d [1]
Inclination 0.199° (to Saturn's equator)
Satellite of Saturn
Physical characteristics
Dimensions 36 × 32 × 30 km
Mean radius 16 km
Rotation period assumed synchronous
Axial tilt zero
Albedo 1.67 ± 0.20 (geometric)[2]

Helene (pronounced /ˈhɛlɨniː/ HEL-ə-nee, sometimes /hɨˈliːniː/ hə-LEE-nee, or as in Greek Ἑλένη) is a moon of Saturn. It was discovered by Pierre Laques and Jean Lecacheux in 1980 from ground-based observations at Pic du Midi Observatory, and was designated S/1980 S 6.[3] In 1988 it was officially named after Helen of Troy, who was the granddaughter of Cronus (Saturn) in Greek mythology.[4] The moon is also designated Saturn XII, a number which it received in 1982, under the designation Dione B,[5] because it is co-orbital with Dione and located in its leading Lagrangian point (L4).


Exploration

The closest images of Helene are from the Cassini spacecraft's 36,000 km fly-by in 2007. Helene will be the target of a much closer fly-by (1800 km) during Cassini's extended mission on 2010 March 3.

Gallery

Voyager 2 image of Helene.

Cassini-Huygens image taken February 2006

References

  1. ^ NASA Celestia
  2. ^ Verbiscer, A.; French, R.; Showalter, M.; and Helfenstein, P.; Enceladus: Cosmic Graffiti Artist Caught in the Act, Science, Vol. 315, No. 5813 (February 9, 2007), p. 815 (supporting online material, table S1)
  3. ^ IAUC 3496: Satellites of Saturn 1980 July 31 (discovery)
  4. ^ IAUC 4609: Satellites of Saturn and Uranus 1988 June 8 (naming the moon)
  5. ^ Transactions of the International Astronomical Union, Vol. XVIIIA, 1982 (mentioned in IAUC 3872: Satellites of Jupiter and Saturn, 1983 September 30)

External links

v • d • e
Moons of Saturn
Generally listed in increasing distance from Saturn. Temporary names in italics.
Ring shepherds
Co-orbitals
Inner large (with Trojans)
Mimas · Enceladus · Tethys (Telesto • Calypso) · Dione (Helene • Polydeuces)
Inner small
Outer large
Inuit group
Norse group
Gallic group
Rings of Saturn · Cassini-Huygens · Themis · Chiron

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Helene (moon)".  Read more