Pi Sagittarii

Pi Sagittarii

Location of π Sagittarii (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Sagittarius
Right ascension	19h 09m 45.83293s
Declination	–21° 01′ 25.0103″
Apparent magnitude (V)	+2.89
Characteristics
Spectral type	F2 II
U−B color index	+0.22
B−V color index	+0.35
Astrometry
Radial velocity (Rv)	–9.8 km/s
Proper motion (μ)	RA: –1.36 mas/yr Dec.: –36.45 mas/yr
Parallax (π)	6.40 ± 0.43 mas
Distance	510 ± 30 ly (160 ± 10 pc)
Details
Mass	5.9 ± 0.3 M☉
Surface gravity (log g)	2.21 ± 0.05 cgs
Temperature	6,590 ± 50 K
Rotational velocity (v sin i)	30 km/s
Age	67 Myr
Other designations
Albaldah, π Sagittarii, π Sgr, Pi Sgr, 41 Sagittarii, BD-21 5275, CCDM J19098-2101AB, FK5 720, GC 26386, HD 178524, HIP 94141, HR 7264, IDS 19038-2111 AB, PPM 269391, SAO 187756, WDS J19098-2101AB.

Pi Sagittarii (Pi Sgr, π Sagittarii, π Sgr) is a triple star system in the zodiac constellation Sagittarius. It has the traditional name Albaldah.

Albaldah has an apparent visual magnitude of +2.89, which is sufficiently bright to be readily seen with the naked eye. Based upon parallax measurements, this star is located at a distance of roughly 510 light-years (160 parsecs) from Earth. Because it is close to the ecliptic, Albaldah can sometimes be occulted by the Moon, and, very rarely, planets of the Solar System. The next occultation by a planet takes place on February 17, 2035, when it will be occulted by Venus.

The spectrum of this star matches a stellar classification of F2 II. The 'II' luminosity class is for a bright giant star that has exhausted the hydrogen at its core and has followed an evolutionary track away from the main sequence of stars like the Sun. Because it has nearly six times the mass of the Sun, it reached this stage in a mere 67 million years. The outer envelope is radiating energy at an effective temperature of about 6,590 K, giving it the yellow-white hue of an F-type star.

Pi Sagittarii has two nearby companions. The first is located at an angular separation of 0.1 arcseconds from Albaldah, or at least 13 Astronomical Units (AU). The second is 0.4 arcseconds away, which is 40 AU or more. Nothing is known about the orbits of these stars.

Name and etymology

• The name Albaldah is comes from the Arabic بلدة bálda 'the town'. In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Nir al Beldat, which was translated into Latin as Lucida Oppidi, meaning the brightest of the town.
• This star, together with ζ Sgr and σ Sgr may have been the Akkadian Gu-shi-rab‑ba, the Yoke of the Sea.
• In Chinese, 建 (Jiàn), meaning Establishment, refers to an asterism consisting of π Sagittarii, ξ² Sagittarii, ο Sagittarii, 43 Sagittarii, ρ¹ Sagittarii and υ Sagittarii. Consequently, π Sagittarii itself is known as 建三 (Jiàn sān, English: the Third Star of Establishment.)