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The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on spiral galaxy distanced 21 million light-years (six megaparsecs)〔 away in the constellation Ursa Major, first discovered by Pierre Méchain on March 27, 1781, and communicated to Charles Messier who verified its position for inclusion in the ''Messier Catalogue'' as one of its final entries. On February 28, 2006, NASA and the ESA released a very detailed image of the Pinwheel Galaxy, which was the largest and most detailed image of a galaxy by Hubble Space Telescope at the time.〔(HubbleSite – NewsCenter – Hubble's Largest Galaxy Portrait Offers a New High-Definition View (02/28/2006) – Introduction )〕 The image was composed from 51 individual exposures, plus some extra ground-based photos. On August 24, 2011, a Type Ia supernova, SN 2011fe, was discovered in M101. == Discovery == Pierre Méchain, the discoverer of Messier 101, described it as a "nebula without star, very obscure and pretty large, 6' to 7' in diameter, between the left hand of Bootes and the tail of the great Bear. It is difficult to distinguish when one lits the () wires."〔(SEDS Historical Notes )〕 William Herschel noted in 1784 that "() in my 7, 10, and 20-feet (length ) reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed."〔 Lord Rosse observed M101 in his 72-inch diameter Newtonian reflector during the second half of the 19th century. He was the first to make extensive note of the spiral structure and made several sketches.〔 To observe the spiral structure in modern instruments requires a fairly large instrument, very dark skies, and a low power eyepiece. 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「Pinwheel Galaxy」の詳細全文を読む スポンサード リンク
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