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Tau Ceti (τ Cet, τ Ceti) is a star in the constellation Cetus that is spectrally similar to the Sun, although it has only about 78% of the Sun's mass. At a distance of just under 12 light-years from the Solar System, it is a relatively nearby star, and is the closest solitary G-class star.〔Alpha Centauri A is closer, but is a member of a triple system.〕 The star appears stable, with little stellar variation, and is metal-deficient. Observations have detected more than ten times as much dust surrounding Tau Ceti as is present in the Solar System. Since December 2012, there has been evidence of possibly five planets orbiting Tau Ceti, with two of these being potentially in the habitable zone. Because of its debris disk, any planet orbiting Tau Ceti would face far more impact events than Earth. Despite this hurdle to habitability, its solar analog (Sun-like) characteristics have led to widespread interest in the star. Given its stability, similarity and relative proximity to the Sun, Tau Ceti is consistently listed as a target for the Search for Extra-Terrestrial Intelligence (SETI), and it appears in some science fiction literature. It can be seen with the unaided eye as a third-magnitude star.〔It can not be observed above latitude 75°N, because that is 90° north of the declination, 15°S. In practice, atmospheric effects will reduce visibility of the object when it is near the horizon.〕 As seen from Tau Ceti, the Sun would be a third-magnitude star in the constellation Boötes.〔From Tau Ceti the Sun would appear on the diametrically opposite side of the sky at the coordinates RA=, Dec=, which is located near Tau Boötis. The absolute magnitude of the Sun is 4.8, so, at a distance of , the Sun would have an apparent magnitude: .〕 ==Name== Tau Ceti does not have a widely-recognized traditional name, and is usually simply referred to as Tau Ceti. The name "Tau Ceti" is the Bayer designation for this star, established in 1603 as part of German celestial cartographer Johann Bayer's ''Uranometria'' star catalogue: it is "number T" in Bayer's sequence of constellation Cetus. It has the proper name Durre Menthor. In the catalogue of stars in the ''Calendarium'' of Al Achsasi al Mouakket, written at Cairo about 1650, this star was designated Thālith al Naʽāmāt (تالت ألنعامة - ''taalit al naʽāmāt''), which was translated into Latin as Tertia Struthionum, meaning ''the third of the ostriches''. This star, along with η Cet (Deneb Algenubi), θ Cet (Thanih Al Naamat), ζ Cet (Baten Kaitos), and υ Cet, were Al Naʽāmāt (ألنعامة), the Hen Ostriches.〔η Cet as Aoul al Naamat or Prima Sthrutionum (the first of the ostriches), θ Cet as Thanih al Naamat or Secunda Sthrutionum (the second of the ostriches), τ Cet as Thalath al Naamat or Tertia Sthrutionum (the third of the ostriches), and ζ Cet as Rabah al Naamat or Quarta Sthrutionum (the fourth of the ostriches). υ Cet should be Khamis al Naamat or Quinta Sthrutionum (the fifth of the ostriches) consistently, but Al Achsasi Al Mouakket designated the title ''the fifth of the ostriches'' to γ Gam with uncleared consideration.〕 In Chinese, the "Square Celestial Granary" () refers to an asterism consisting of τ Ceti, ι Ceti, η Ceti, ζ Ceti, θ Ceti and 57 Ceti. Consequently, τ Ceti itself is known as the "Fifth Star of Square Celestial Granary" (). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tau Ceti」の詳細全文を読む スポンサード リンク
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