Magnitude 3.89 Apparent magnitude (V) 3.89 | ||
 | ||
Similar Pi Herculis, Theta Herculis, Kappa Herculis | ||
Tau Herculis (τ Her, τ Herculis) is a fourth-magnitude star in the constellation Hercules. Its traditional name Rukbalgethi Shemali, though seldom used today in scientific journals, means the "northern knee". It is a blue subgiant star, seven hundred times more luminous than the Sun.
Contents
Properties
Tau Herculis is a blue subgiant star with stellar classification B5IV. Its mass is 4.9 times solar. Though its apparent magnitude is only 3.89, like all B-class stars, it is very luminous boasting a total bolometric luminosity that is 700 times solar. Hipparcos estimated its distance at roughly 96 parsecs from Earth, or 310 ± 20 light years away.
Etymology
Its traditional name Rukbalgethi Shemali is of Arabic origin and shares certain etymological characteristics with the stars Ruchbah and Zubeneschamali signifying Hercules' "northern knee". The star was the north pole star around the year 7400 BC, a phenomenon which is expected to reoccur in the year 18,400 due to precession.
In Chinese, 七公 (Qī Gōng), meaning Seven Excellencies, refers to an asterism consisting of τ Herculis, 42 Herculis, φ Herculis, χ Herculis, ν1 Boötis, μ1 Boötis and δ Boötis. Consequently, τ Herculis itself is known as 七公二 (Qī Gōng èr, English: the Second Star of Seven Excellencies.)