vendredi 19 septembre 2008

Lyra 7

Gamma Lyrae (γ Lyr / γ Lyrae) is a star in the constellation Lyra. It also has the traditional names السلحفاة Sulafat or Sulaphat (arab. "turtle"), or Jugum (lat. iugum, "yoke, Kummet").
It has spectral class A0 and is of magnitude 3.3.
Gamma Lyrae is approximately 635 light years from Earth.
Coordinates (epoch J2000):
Right ascension: 18h58m56s
Declination: +32°41'22"
Beta Lyrae (β Lyr / β Lyrae) is a binary star system approximately 882 light-years away in the constellation Lyra. Beta Lyrae is traditionally named الشلياق Sheliak which is Arabic for "tortoise" or "harp." Beta Lyrae is an eclipsing contact binary star system made up of a blue-white dwarf (B7V) star and a white main sequence (A8V) star. The two stars are close enough that material from the photosphere of each is pulled towards the other, drawing the stars into an ellipsoid shape. Beta Lyrae is the prototype for this class of eclipsing binaries, whose components are so close together that they deform by their mutual gravitation.
Beta Lyrae changes its apparent magnitude from +3.4 to +4.6 over a period of 12.9075 days. The two components of the main star are so close together that they cannot be resolved with optical telescopes, forming a spectroscopic binary.
The system also has a third star, at an angular distance of 45.7", which is of spectral type B7V and has an apparent magnitude of +7.2 and can easily be seen with binoculars. It is about 80 times as luminous as the Sun and is also a spectroscopic binary with a period of 4.34 days. There is also another star that appears to be in the Beta lyrae system, F, magnitude 9.9v separation 86" and luminosity 7 times that of the Sun.
Eta Lyrae (η Lyr / η Lyrae) is a star in the constellation Lyra. It also has the traditional name Aladfar (Arabic for "claws").
Eta Lyrae belongs to spectral class B2.5IV and has apparent magnitude of +4.39. It is approximately 1040 light years from Earth.
Coordinates (equinox J2000.0)
Right ascension: 19h13m45.50s
Declination: +39°08'46.0"

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