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The North America Nebula (NGC 7000 or Caldwell 20) is an emission nebula in the constellation Cygnus, close to Deneb (the tail of the swan and its brightest star). The remarkable shape of the nebula resembles that of the continent of North America, complete with a prominent Gulf of Mexico. It is sometimes incorrectly called the "North ''American'' Nebula".〔(【引用サイトリンク】url=http://www.nasa.gov/mission_pages/spitzer/news/spitzer20110210.html )〕 ==General information== The North America Nebula is large, covering an area of more than four times the size of the full moon; but its surface brightness is low, so normally it cannot be seen with the unaided eye. Binoculars and telescopes with large fields of view (approximately 3°) will show it as a foggy patch of light under sufficiently dark skies. However, using a UHC filter, which filters out some unwanted wavelengths of light, it can be seen without magnification under dark skies. Its prominent shape and especially its reddish color (from the hydrogen Hα emission line) show up only in photographs of the area. Cygnus's Wall is a term for the "Mexico and Central America part" of the North America Nebula. The Cygnus Wall exhibits the most concentrated star formations in the nebula. The North America Nebula and the nearby Pelican Nebula, (IC 5070) are in fact parts of the same interstellar cloud of ionized hydrogen (H II region). Between the Earth and the nebula complex lies a band of interstellar dust that absorbs the light of stars and nebulae behind it, and thereby determines the shape as we see it. The distance of the nebula complex is not precisely known, nor is the star responsible for ionizing the hydrogen so that it emits light. If the star inducing the ionization is Deneb, as some sources say, the nebula complex would be about 1800 light years distance, and its absolute size (6° apparent diameter on the sky) would be 100 light years. The nebula was discovered by William Herschel on October 24, 1786, from Slough, England. Image:North-America-nebula.jpeg|Amateur photo. Image:Nord america.jpg| Image:North America Nebula.jpg|Infrared view of the nebula. File:The North America Nebula.ogv|The North America Nebula. 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「North America Nebula」の詳細全文を読む スポンサード リンク
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