[2017年10月20日: 美丽的三叶星云-（A Beautiful Trifid）--原图下载](https://apod.nasa.gov/apod/image/1710/m020_rooisand_cdk_3500x2500.jpg"
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Image Credit &Copyright: ChamaeleonTeam -Franz Hofmann, Wolfgang Paech
说明: 美丽的三叶星云是研究宇宙天体色泽对比的好标的。三叶星云亦称为M20，位在星云群聚的人马座内，离我们约有5,000光年远。三叶星云是我们银河系盘面上的一个恒星形成区，同时拥有三种形态的天文星云，包括被氢原子辉光渲染成红色的发射星云、尘埃反射星光所形成的蓝色反射星云、及緻密尘埃云所造成的黝黑剪影状暗星云。在遮光尘埃带的切割下，明亮的发射星云被分割成三片，让它得到三叶星云的令名。在星云中心的左下方，受到新恒星雕塑的云气柱及恒星喷流，曾是哈伯太空望远镜为此区域拍摄的着名特写影像之标的。三叶星云的跨幅约有40光年，在地球的天空中涵盖的区域和月亮相当，不过它过于昏暗，因此肉眼不得见。
原文：
Image Credit &Copyright: ChamaeleonTeam -Franz Hofmann, Wolfgang Paech
Explanation: The beautifulTrifid Nebula is acosmic study in contrasts.Also known as M20, it lies about5,000light-years away toward the nebula richconstellation Sagittarius.A star forming region in the plane of our galaxy,the Trifid does illustrate three different types ofastronomical nebulae;red emission nebulae dominated bylight from hydrogen atoms,blue reflection nebulae producedby dust reflecting starlight, anddark nebulae wheredense dust clouds appear in silhouette.But the red emission region roughly separated into threeparts by obscuring dust lanes is what lends the Trifid itspopular name.Pillars and jets sculpted by newborn stars, below and left ofthe emission nebula's center, appear in famous Hubble Space Telescopeclose-upimages of the region.The Trifid Nebula is about 40 light-years across.Just too faint to be seen by the unaided eye, it almost covers thearea of the Moonin planet Earth's sky.
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