2018年08月24日:梅西叶20与21-（Messier 20 and 21）--原图下载
Image Credit &Copyright:IgnacioDiaz Bobillo
说明: 亦名为M20的美丽三叶星云，位在星云密布的人马座之内，是一个小望远镜轻易可见的天体。在这张跨幅1度的影像里，距离约5,000光年远的三叶星云，与右下角的疏散星团M21分享了这片取景佳妙的视野，构成了探索天体对比的多彩案例。受到尘埃带分割的三叶星云，大小约为40光年，年龄则在30万年左右。因此，它是我们天空中最年轻的恒星形成区之一，其内的新生恒星和胎星仍然包裹在孕育它们的尘埃和云气里。而估计距离和M20相当的疏散星团M21，内部的恒星之年龄是远为年长的8百万年。虽然它们分享了这片壮丽的望远镜星野，不过，它们二者之间并无明显的关联。
原文：
Image Credit &Copyright:IgnacioDiaz Bobillo
Explanation: The beautiful Trifid Nebula,also known as Messier 20, is easytofind with a small telescope in the nebula rich constellation Sagittarius.About 5,000 light-years away, the colorful study incosmic contrasts sharesthiswell-composed, nearly 1 degree wide field withopen star clusterMessier 21(bottom right).Trisected by dust lanesthe Trifid itself is about 40 light-years across anda mere 300,000 years old.That makes it one of theyoungest starformingregions in our sky,with newborn and embryonic stars embedded in itsnatal dust and gas clouds.Estimates of the distance to open star cluster M21 are similar to M20's,but though they share this gorgeous telescopic skyscapethere is no apparent connection between the two.In fact, M21's stars are much older, about 8 millionyearsold.
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