Magnitude 4.48 Apparent magnitude (V) 4.48 | ||
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Sigma Hydrae (σ Hydrae, σ Hya) is the Bayer designation for a solitary star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.48. The estimated distance to this star, based upon an annual parallax shift of 8.75 mas, is around 370 light years. At that distance, the visual magnitude of the star is diminished by an interstellar extinction factor of 0.16, due to intervening dust.
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This is an evolved K-type giant star with a stellar classification of K2 III. The measured angular diameter of this star, after correction for limb darkening, is 7000225000000000000♠2.25±0.03 mas. At the estimated distance of this star, this yields a physical size of about 27.6 times the radius of the Sun. It has about three times the mass of the Sun and radiates 295 times the solar luminosity from its outer atmosphere at an effective temperature of 4,491 K. Sigma Hydrae is around 430 million years old.
Etymology
It is also known by the proper name Minchir, and appears as Minchir es-schudscha' on Bode's large star atlas, Uranographia, which is derived from the Arabic Minkhir al-Shuja‘, "the Nostril of Hydra", for this star. The name is erroneously spelt as Al Minliar al Shuja in the Yale Bright Star Catalogue.[1].
This star, along with δ Hya (Lisan al Shudja), ε Hya, ζ Hya, η Hya and ρ Hya, were Ulug Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".
According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Min al Azʽal or Minazal were the title for five stars : δ Hya as Minazal I, η Hya as Minazal II, ε Hya as Minazal III, ρ Hya as Minazal IV and ζ Hya as Minazal V (exclude this star)
In Chinese, 柳宿 (Liǔ Sù), meaning Willow (asterism), refers to an asterism consisting of σ Hydrae, δ Hydrae, η Hydrae, ρ Hydrae, ε Hydrae, ζ Hydrae, ω Hydrae and θ Hydrae Consequently, σ Hydrae itself is known as 柳宿二 (Liǔ Sù èr, English: the Second Star of Willow.).
The people of Groote Eylandt, called Unwala, "The Crab", for the star cluster including this star, δ Hya (Lisan al Shudja), ε Hya, ζ Hya, η Hya and ρ Hya.