Tuesday 19 September 2017 - 08:27:56 Posted by  Bobby

 Mythology of Crux

Crux is the smallest constellation in the sky, it covers a mere 5 percent of the area of the largest constellation, Hydra. Nevertheless, it is one of the most famous and easily recognized star pattern of all. To the ancient Greeks, its stars formed part of the hind legs of Centaurus, the centaur. Crux became a recognized constellation in its own right in the late 16th century as Europeans explored the southern oceans, although no one is credited with its invention. It lies in a brilliant region of the Milky Way. Its longer axis points to the south celestial pole.

 The Facts

  • Depiction: The Southern Cross
  • Pronounced: kruks
  • Genitive: Crucis
  • Abbreviation: Cru
  • Highest in the Sky: April to May
  • Size Ranking: 88th
  • Coverage Area: 68 Sq. Degrees
  • Right Acension: 12 hours
  • Declination: -60°
  • Visibility: 22°N to 90°S

 Notable Objects

  • Alpha Crucis: Double star
  • Beta Crucis: Blue-white giant star
  • Gamma Crucis: Wide optical double star
  • Iota Crucis: Wide double star
  • Mu Crucis: Wide optical double star
  • NGC 4755:(Jewel Box) Open cluster
  • The Coalsack: Dark Nebula

 Named Stars

  • Acrux, Alpha Crucis
  • Mimosa, Beta Crucis
  • Gacrux, Gamma Crucis

 Best Viewed Objects/Stars

Alpha Crucis

 A double star, appearing to the naked eye as a single object of magnitude 0.8, the 13th brightest star in the sky. A small telescope divides it into a glittering blue-white pair, of magnitudes 1.3 and 1.8. Both stars are 320 light-years away and probably form a true binary, although the orbital period is unknown. There is a much wider 5th magnitude star, visible through binoculars, which is not related.

Beta Crucis

 A blue-white giant, lying 350 light-years away. At magnitude 1.3, it is among the 20 brightest stars in the sky. It pulsates in size five times a day, varying by under a tenth of a magnitude as it does so, not enough to be noticeable to the naked eye.

Gamma Crucis

 A wide optical double star. The brighter star is a red giant of magnitude 1.6, 88 light-years away. Binoculars show an unrelated 6th magnitude companion, which is over three times more distant.

Iota Crucis

 A wide double star, components of magnitudes 4.7 and 9.5 that can be separated with a small telescope.

Mu Crucis

 A wide optical double. A small telescope, or powerful binoculars, show the two stars, of magnitudes 4.0 and 5.1. The fainter component is a rapidly rotating star that throws off rings of gas, causing occasional small variations in its brightness.

NGC 4755 (The Jewel Box, The Kappa Crucis cluster)

 A magnificent open cluster, visible to the naked eye as a bright knot in the Milky Way between Beta Crucis and the Coalsack. It is, in fact, far more distant than either of them, lying about 6,500 light-years away. Binoculars or a small telescope show its individual stars, of 6th magnitude and fainter, covering an area of sky about one-third the apparent size of the full Moon. Most of its stars are blue-white super giants, although near its center there is a prominent red supergiant of 8th magnitude. The star near the center of the cluster that is actually designated Kappa Crucis is a blue-white supergiant of magnitude 5.9.

The Coalsack

 A prominent dark nebula, a wedge-shaped cloud of dust and gas about 600 light-years away that blots out the light from the stars in the Milky Way behind it. The Coalsack is large enough for 13 full Moons to be lined up across it. It has no NGC or other catalog number. Although the Coalsack lies mainly in Crux, it spills over the borders of Crux into Centaurus and Musca.


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