- Sigma Sagittarii
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Sigma Sagittarii 
Nunki is the σ star in the constellation of Sagittarius.Observation data
Epoch J2000 Equinox J2000Constellation Sagittarius Right ascension 18h 55m 15.93s [1] Declination –26° 17′ 48.2″ [1] Apparent magnitude (V) 2.05 Characteristics Spectral type B2.5 V U−B color index -0.75 B−V color index -0.22 Variable type ? Astrometry Radial velocity (Rv) -11 km/s Proper motion (μ) RA: 15.14 ± 0.29 [1] mas/yr
Dec.: -53.43 ± 0.19 [1] mas/yrParallax (π) 14.32 ± 0.29[1] mas Distance 228 ± 5 ly
(70 ± 1 pc)Absolute magnitude (MV) -2.14 Details Mass 7 M☉ Radius 5 R☉ Luminosity 3,300 L☉ Temperature 20,000 K Metallicity ? Rotation 201 km/s. Age ? years Other designations Sigma Sagittarii (σ Sgr, σ Sagittarii) is the second brightest star system in the constellation Sagittarius.
Its modern name Nunki is an Assyrian or Babylonian name recovered by archaeologists and made public by R.H.Allen.[2]
Nunki has an apparent magnitude of +2.1 and belongs to the spectral classification B3. The total luminosity of σ Sgr is 3300 times that of the Sun while it has a mass of roughly 7 solar masses. The radius of the star is equivalent to 5 Suns and it has a surface temperature of 20,000 kelvins. Sigma Sgr has a magnitude +9.5 companion, Sigma Sagittarii B, located 5.2 arcminutes away. It may also have a closer companion.
Because it is close to the ecliptic, Nunki can be occulted by the Moon and very rarely by planets. The last occultation of Nunki by a planet took place on November 17, 1981, when it was occulted by Venus.
Furthermore, Nunki is the brightest star that can be principally occulted by an exterior planet. However, only Mars can do this, and only rarely; the last time was on 3 September 423.
References
- ^ a b c d e van Leeuwen, F. (2007). "HIP 92855". Hipparcos, the New Reduction. http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=92544. Retrieved 2009-12-13.
- ^ p.359, Richard Hinckley Allen, "Star Names, their lore and meaning".
External links
Bayer α (Rukbat) • β¹ (Arkab Prior) • β² (Arkab Posterior) • γ¹ • γ² (Alnasl) • δ (Kaus Media) • ε (Kaus Australis) • ζ (Ascella) • η • θ¹ • θ² • ι • κ¹ • κ² • λ (Kaus Borealis) • μ (Polis) • ν¹ (Ain al Rami) • ν² • ξ¹ • ξ² • ο • π (Albaldah) • ρ¹ • ρ² • σ (Nunki) • τ • υ • φ (Nanto) • χ¹ • χ² • χ³ • ψ • ω • b¹ • c • d • e¹ • e² • f • g • h¹ • h² • AFlamsteed 3 • 4 • 6 • 7 • 9 • 10 (γ², Alnasl) • 11 • 13 (μ, Polis) • 14 • 15 • 16 • 17 • 18 • 19 (δ, Kaus Media) • 20 (ε, Kaus Australis) • 21 • 22 (λ, Kaus Borealis) • 24 • 25 • 26 • 27 (φ, Nanto) • 28 • 29 • 30 • 32 (ν¹, Ain al Rami) • 33 • 34 (σ, Nunki) • 35 (ν²) •36 (ξ¹) • 37 (ξ²) • 38 (ζ, Ascella) • 39 (ο) • 40 (τ) • 41 (π, Albaldah) • 42 (ψ) • 43 (d) • 44 (ρ¹) • 45 (ρ²) • 46 (υ) • 47 (χ¹) • 48 (χ²) • 49 (χ³) • 50 • 51 (h¹) • 52 (h²) • 53 • 54 (e¹) • 55 (e²) • 56 (f) • 57 • 58 (ω) • 59 (b¹) • 60 (A) • 61 (g) • 62 (c) • 63 • 65 • 63 OphNearby Ross 154 • Gliese 783 • Gliese 745Other Categories:- Bayer objects
- Sagittarius constellation
- Binary stars
- B-type main sequence stars
- Stars with proper names
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