2017年06月28日:梅西叶20与21的组合影像-（Composite Messier 20 and 21）--原图下载
Image Credit &Copyright: Martin Pugh
说明: 距离约5,000光年远、亦名为M20的美丽三叶星云，是一个探索天体对比的多彩案例。在这张跨幅1度的影像里，它与左上角的疏散星团M21分享了这片视野。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，其内部的新生恒星和胎星仍然包裹在孕育它们的尘埃和云气里。而疏散星团M21内的恒星之年龄是远为年长的8百万年；虽然它的估计距离也和M20相当，更分享这片壮丽的望远镜星野，不过它们之间并无明显的关联。M20和M21都是用小望远镜，就可以轻易在满布星云的人马座之内找到的天体。这幅使用2部不同的望远镜所拍摄的影像，则组合了高分辨率的窄波段M20照片和另一张涵盖M21的较大视野照片。
原文：
Image Credit &Copyright: Martin Pugh
Explanation: The beautiful Trifid Nebula,also known as Messier 20, lies about 5,000 light-years away, acolorful study in cosmic contrasts.It shares this nearly 1 degree wide field withopen star clusterMessier 21(top left).Trisected by dust lanesthe Trifid itself is about 40 light-years across anda mere 300,000 years old.That makes it one of theyoungest starforming regions in our sky, with newborn and embryonic stars embeddedin its natal 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.M21's stars are much older, about 8 millionyearsold.M20 and M21 are easytofind with even a small telescope in the nebula rich constellationSagittarius.In fact, this well-composed scene is acomposite from two different telescopes.Using narrowband data it blends a high resolution image of M20 with awider field image extending to M21.
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