dimanche 31 août 2008

Corvus 1


A small southern constellation with only 11 stars visible to the naked eye (brighter than magnitude 5.5). It was one of the 48 constellations listed by Ptolemy, who only counted 7 stars.


Gamma Corvi (γ Crv / γ Corvi) est l'étoile la plus brillante de la constellation du Corbeau. Son nom traditionnel est Gienah, cependant Epsilon Cygni porte également le même nom. Le nom "Gienah Corvi" (ou "Gienah Ghurab") peut être utilisé pour la distinguer de Gienah du Cygne.


"Gienah" vient de l'arabe, de la phrase d'Ulugh Beg الجناح الغراب اليمن al-janāħ al-ghirāb al-yaman, signifiant "l'aile droite du corbeau", bien que sur les cartes modernes elle indique l'aile gauche.



γ Crv


Gienah
Al-Janah
The wing
جناح



β Corvi


KRAZ (Beta Corvi). We learn in beginning astronomy that Johannes Bayer listed the stars by Greek letters according to their brightness within a constellation. Then we see constellations like Corvus (the Crow) and learn of the many exceptions. While bright third magnitude (2.65) Kraz, Beta Corvi, is indeed number two as expected, for reasons no one will know, Gienah (Gamma Corvi) tops the list, the Alpha star (Alchiba) ranking a miserable fourh-magnitude fifth. The proper name is no less mysterious. Assigned in modern times, no one seems to know just what it means (though one source claims "left-handed lynch pin"). Suggestions or sources from readers are welcome: a contest (with no prizes save that we will know). Physically, the star is a yellow-white class G (G5) bright giant very much like (but more luminous than) Mu Velorum, which lies not terribly far away. From its distance of 140 light years, this 5100 Kelvin star radiates with the power of 160 Suns, which together give a radius of 16 solar. Though the star's (minimum) equatorial rotation speed is just over double that of the Sun's, its large size means that it may take as much as 180 days to make a full turn. The luminosity and temperature also conspire to give us a calculated mass of 3.3 solar. Kraz is also seen to be a rather rare "star in transition," one with a quiet helium core that has nearly completed its conversion into a fully-blown giant five times brighter than now, after which the helium core will light up and fuse to carbon, which will stabilize the star for a time at a somewhat dimmer luminosity. Kraz appears to be all alone, with no observed companion. However the star is also listed as a "weak" barium star. Such stars are giants that were chemically contaminated by more-massive companions that brought by-products of nuclear reactions to their surfaces, passed them to their unevolved mates (the stars we now see), and that have now shrunk to white dwarf status. Most likely the classification is spurious, and Kraz really is by itself. Some 300 million years ago, Kraz (whatever it means) shone as a lovely blue- white class B7 star. It will one day become a relatively massive, though lonely, white dwarf itself, one that will never have the chance to chemically enrich its own companion.

Delta Corvi (δ Crv / δ Corvi) is a star in the constellation Corvus. It also has the traditional name Algorab. It is known as 軫宿三 (the Third Star of the Chariot) in Chinese.
Alpha Corvi (α Crv / α Corvi) is a star in the constellation Corvus. It also has the traditional names Alchiba (Arabic "tent") or Al Minliar al Ghurab. It is known as 右轄 (the Right Linchpin) in Chinese.
Alchibah
Al-Khiba'
The tent
الخباء

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