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〕 | epoch = J2000 | type = dSph(t) | ra = 〔 | dec = 〔 | dist_ly = 65 ± 7 kly (20 ± 2 kpc) | z = 140 ± ? km/s〔 | appmag_v = 4.5〔 | size_v = 450′.0 × 216′.0〔 | constellation name = Sagittarius | notes = Heading for a collision with the Milky Way | names = Sag DEG,〔(Sagittarius Dwarf Elliptical Galaxy / Sag DEG )〕 Sgr dSph,〔 Sagittarius Dwarf Spheroidal,〔 Sgr I Dwarf〔 }} The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It consists of four globular clusters, the main cluster having been discovered in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit (i.e. an orbit passing through the galactic poles) at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large Magellanic Cloud). In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past. Sgr dSph should not be confused with the Sagittarius Dwarf Irregular Galaxy, or the Sag DIG, a small galaxy 3.4 million light-years distant. ==Features== Officially discovered in 1994, by , Mike Irwin, and Gerry Gilmore, Sgr dSph was immediately recognized as being the nearest known neighbor to our Milky Way at the time. (Since 2003, the newly discovered Canis Major Dwarf Galaxy is considered the actual nearest neighbor). Although it is one of the closest companion galaxies to the Milky Way, the main parent cluster is on the opposite side of the galactic core from Earth, and consequently is very faint, although it covers a large area of the sky. Sgr dSph appears to be an older galaxy, with little interstellar dust and composed largely of Population II stars, older and metal-poor, as compared to the Milky Way. No neutral hydrogen gas related to Sgr dSph has been found. Further discoveries by astrophysics teams from both the University of Virginia and the University of Massachusetts Amherst, drawing upon the 2MASS Two-Micron All Sky Infrared Survey data, revealed the entire loop-shaped structure. In 2003 with the aid of infrared telescopes and super computers, Steven Majewski, Michael Skrutskie, and Martin Weinberg were able to help create a new star map, picking out the full Sagittarius Dwarf presence, position, and looping shape from the mass of background stars and finding this smaller galaxy to be at a near right angle to the plane of the Milky Way.〔http://www.astro.virginia.edu/~mfs4n/sgr/sgr_big.jpg〕 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「Sagittarius Dwarf Spheroidal Galaxy」の詳細全文を読む スポンサード リンク
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