Alpha Librae

α Librae
Location of α Librae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Libra
α1 Lib
Right ascension 14h 50m 41.18097s[1]
Declination −15° 59′ 50.0482″[1]
Apparent magnitude (V) +5.153[2]
α2 Lib
Right ascension 14h 50m 52.71309s[1]
Declination −16° 02′ 30.3955″[1]
Apparent magnitude (V) +2.741[2]
Characteristics
α1 Lib
Spectral type F3 V[3]
U−B color index −0.02[4]
B−V color index +0.39[4]
α2 Lib
Spectral type kA2hA5mA4 IV-V[5]
U−B color index +0.10[4]
B−V color index +0.15[4]
Astrometry
α1 Lib
Radial velocity (Rv)−23.47[6] km/s
Proper motion (μ) RA: −136.27[1] mas/yr
Dec.: −59.04[1] mas/yr
Parallax (π)43.52 ± 0.43 mas[1]
Distance74.9 ± 0.7 ly
(23.0 ± 0.2 pc)
Absolute magnitude (MV)+3.35[7]
α2 Lib
Proper motion (μ) RA: −105.68[1] mas/yr
Dec.: −68.40[1] mas/yr
Parallax (π)43.03 ± 0.19 mas[1]
Distance75.8 ± 0.3 ly
(23.2 ± 0.1 pc)
Orbit[6]
Period (P)70.34 days
Semi-major axis (a)0.51 au
Eccentricity (e)0.41
Semi-amplitude (K2)
(secondary)		43.1 km/s
Details
α1 Lib
Mass1.4–1.5/0.5–0.6[8] M☉
Radius1.409[9][a] R☉
Surface gravity (log g)4.25[5] cgs
Temperature6,653[7] K
Metallicity [Fe/H]−0.07[7] dex
Rotational velocity (v sin i)5.95[10] km/s
Age1.1+0.6
−0.8[7] Gyr
α2 Lib
Mass1.95 / 1.79[11] M☉
Radius2.21 / 1.92[11] R☉
Surface gravity (log g)3.91[5] cgs
Temperature8,200 / 7,930[11] K
Metallicity [Fe/H]−0.24[5] dex
Other designations
Zubenelgenubi, Kiffa Australis, Lanx Australis, α Lib.
α1 Lib: 8 Librae, BD−15 3965, FK5 1387, HD 130819, HIP 72603, HR 5530, SAO 158836.[12]
α2 Lib: 9 Librae, BD−15 3966, FK5 548, HD 130841, HIP 72622, HR 5531, SAO 158840.[13]
Database references
SIMBADα Lib
α1 Lib
α2 Lib

Alpha Librae (α Librae, abbreviated Alpha Lib, α Lib) is a double star and, despite its 'alpha' designation, it is the second-brightest star system (or star) in the constellation of Libra. The two components are designated α1 Librae and α2 Librae. The system bore the traditional name of Zubenelgenubi /zuːˌbɛnɛldʒɪˈnuːbi/,[14] though the International Astronomical Union now regards that name as only applying to α2 Librae.[15]

Alpha2 Librae is 0.33 degrees north of the ecliptic so it can be occulted by the Moon and (very rarely) by planets. It was occulted by Venus on October 25, 1947;[16] the next occultation by a planet will be by Mercury on 10 November 2052.[17] Both components are eclipsed (occulted) by the sun from about 7–9 November.[18] Thus the star can be viewed the whole night, crossing the sky, in early May.

  1. ^ a b c d e f g h i j Cite error: The named reference aaa474_2_653 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference sps1966 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference mk was invoked but never defined (see the help page).
  4. ^ a b c d Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  5. ^ a b c d Cite error: The named reference apj132_1_161 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference orbit was invoked but never defined (see the help page).
  7. ^ a b c d Cite error: The named reference aaa501_3_941 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference aaa514_A98 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference cruzalebes was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference aaa520_A79 was invoked but never defined (see the help page).
  11. ^ a b c Cite error: The named reference waisberg was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference SIMBAD1 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference SIMBAD2 was invoked but never defined (see the help page).
  14. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  15. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  16. ^ Cite error: The named reference Koennen1981 was invoked but never defined (see the help page).
  17. ^ Peuschel, Marco (2003). "Astronomische Ereignisse der besonderen Art" Archived 2005-03-16 at the Wayback Machine. Retrieved July 10, 2005.
  18. ^ In the Sky Earth astronomy reference utility showing the ecliptic and relevant date as at J2000 - present


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