Astronomy Picture of the Day——梅西耶天体20和21

Messier 20 and 21 
Image Credit & Copyright: Stanislav Volskiy, Chilescope Team

Explanation: The beautiful Trifid Nebula, also known as Messier 20, is easy to find with a small telescope in the nebula rich constellation Sagittarius. About 5,000 light-years away, the colorful study in cosmic contrasts shares this well-composed, nearly 1 degree wide field with open star cluster Messier 21 (top left). Trisected by dust lanes the Trifid itself is about 40 light-years across and a mere 300,000 years old. That makes it one of the youngest star forming regions in our sky, with newborn and embryonic stars embedded in 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 skyscape there is no apparent connection between the two. In fact, M21's stars are much older, about 8 million years old.

梅西耶天体20和21

也被命名为M20的美丽三叶星云位于星云密布的人马座，使用小型望远镜就能看到它。在这幅跨度将近1度的合成照片中，距离地球约5000光年的三叶星云与位于左上方的疏散星团M21形成了鲜明的对比。三叶星云的大小约40光年，拥有30万年的历史，被尘埃带分割为三部分。它是天空中最年轻的恒星形成区之一，新生恒星被包裹在孕育它们的尘埃和气体云中。疏散星团M21的距离与M20相当，尽管它们共享这片壮丽的星野，但是两者之间并没有明显的关系。实际上，M21中的恒星要古老得多，大约有800万年的历史。

高清原图地址：

https://apod.nasa.gov/apod/image/1912/M20_volskiy.jpg

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