Beta Lyrae

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**Beta Lyrae AB**
Observation data Epoch J2000.0
Constellation	Lyra
Right ascension	18^h 50^m 04.8^s
Declination	+33° 21′ 46″
Apparent magnitude (V)	3.52 (3.4–4.3)
Spectral Characteristics
Spectral type	B7Ve/A8Vp
U-B color index	−0.56
B-V color index	0.00
Variable type	β Lyr
Astrometry
Radial velocity (R_v)	−19.2 km/s
Proper motion (μ)	RA: 1.10 mas/yr Dec.: −4.46 mas/yr
Parallax (π)	3.70 ± 0.52 mas
Distance	approx. 900 ly (approx. 270 pc)
Absolute magnitude (M_V)	−3.91
Physical Characteristics
Mass	2/12 M_☉
Radius	19/15 R_☉
Luminosity	2,000 L_☉
Temperature	13,000/8,000 K
Metallicity	?
Rotation	?
Age	? years
Other designations
Sheliak, 10 Lyrae, HR 7106, BD+33°3223, HD 174638, SAO 67451, AAVSO 1846+33, FK5 705, HIP 92420

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 Sheliak which is Arabic for "Harp."

Animation showing how the light curve of a contact binary star changes as they orbit.

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 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. On the other hand the two components of the main star are so close together that they cannot be resolved with optical telescopes, forming a spectroscopic binary.