Nu Scorpii (ν Scorpii, abbreviated Nu Sco, ν Sco) is a multiple star system in the constellation of Scorpius. It is most likely a septuple star system,^[5] consisting of two close groups (designated Nu Scorpii AB and CD) that are separated by 41 arcseconds.^[5] Based on parallax measurements,^[7] it is approximately 470 light-years from the Sun.

Quick Facts Apparent magnitude (V), Characteristics ...

ν Scorpii

Location of ν Sco (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Scorpius
ν Sco A
Right ascension	16h 11m 59.740s[1]
Declination	−19° 27′ 38.33″[1]
Apparent magnitude (V)	4.349[1]
ν Sco B
Right ascension	16h 11m 59.746s[2]
Declination	−19° 27′ 36.94″[2]
Apparent magnitude (V)	6.60[2]
ν Sco CD
Right ascension	16h 11m 58.603s[3]
Declination	−19° 27′ 00.15″[3]
Apparent magnitude (V)	6.30[4]
Characteristics
ν Sco AB
Spectral type	B3V[5] / ? / ? / ?
U−B color index	–0.63[4]
B−V color index	+0.05[4]
ν Sco CD
Spectral type	B9III[5] / B9III[5] / ?
U−B color index	–0.37[4]
B−V color index	+0.13[4]
Astrometry
ν Sco AB
Radial velocity (Rv)	2.4 ± 5[6] km/s
Proper motion (μ)	RA: –7.65[7] mas/yr Dec.: –23.71[7] mas/yr
Parallax (π)	6.88 ± 0.76 mas[7]
Distance	approx. 470 ly (approx. 150 pc)
ν Sco CD
Radial velocity (Rv)	–14 ± 5[6] km/s
Proper motion (μ)	RA: –4.2[3] mas/yr Dec.: –18.0[3] mas/yr
Orbit[8]
Primary	ν Sco Aa
Companion	ν Sco Ab
Period (P)	5.55206 ± 0.00003
Eccentricity (e)	0.11 ± 0.05
Periastron epoch (T)	2442185.555 ± 0.349
Argument of periastron (ω) (secondary)	267 ± 23°
Semi-amplitude (K1) (primary)	26.5 ± 1.3 km/s
Other designations
Jabbah, ν Sco, 14 Sco, ADS 9951 AB, CCDM J16120-1928AB[9]
ν Sco AB: BD–19° 4333, HD 145502, HIP 79374, HR 6027, SAO 159764[9]
ν Sco CD: BD–19° 4332, HD 145501, HR 6026, SAO 159763[10]
Database references
SIMBAD	ν Sco
	ν Sco A
	ν Sco B
	ν Sco CD

Close

The component Nu Scorpii Aa is formally named Jabbah /ˈdʒæbə/.^[11] (Contrast the similar-sounding Dschubba, Delta Scorpii.)

Nu Scorpii is the system that causes the reflection nebula cataloged as IC 4592 and known as the Blue Horsehead nebula. Reflection nebulae are actually made up of very fine dust that normally appears dark but can look quite blue when reflecting the light of energetic nearby stars.^[12]

Since it is near the ecliptic, Nu Scorpii can be occulted by the Moon and, very rarely, by planets. Mercury occulted it on 14 December 1821, but will not occult it again until 2 December 2031. The last occultation by Venus took place on 27 December 1852 and the next will take place on 30 December 2095. On 29 July 1808 there was an occultation by Neptune.^{[citation needed]}

ν Scorpii (Latinised to Nu Scorpii) is the system's Bayer designation. The designations of its two constituent groups as Nu Scorpii AB and CD; of the component Nu Scorpii Aa, and of other components similarly lettered, derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).^[13]

Nu Scorpii bore the traditional name Jabbah, possibly from the Arabic Iklīl al Jabhah (إكليل الجبهة 'the crown of the forehead').^[14][15] In 2016, the IAU organized a Working Group on Star Names (WGSN)^[16] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.^[17] It approved the name Jabbah for the component Nu Scorpii Aa on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.^[11]

In Chinese astronomy, Nu Scorpii is called 鍵閉, Pinyin: Jiànbì, meaning Door Bolt, because it is marking itself and standing alone in the Door Bolt asterism, Room mansion (see : Chinese constellations).^[18] 鍵閉 (Jiànbì), westernized into Keen Pi, but that name (meaning "the Two Parts of a Lock") was ascribed to the pair Lambda Scorpii (Shaula) and Upsilon Scorpii (Lesath) by R.H. Allen.^[15]

Nu Scorpii is a septuple star system.^[5] It is one of only two such known systems, the other being AR Cassiopeiae. Higher-multiplicity star systems are uncommon because they are less stable than their simpler counterparts, and often decay into smaller systems.

Nu Scorpii is split into two groups, Nu Scorpii AB and Nu Scorpii CD. Nu Scorpii CD is located 41 arcseconds away from Nu Scorpii A, and is also known as HR 6026.^[10]