Messier 20 and 21
Image Credit & Copyright:
Emanuele Petrilli

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 (right). 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.

Tomorrow’s picture: dark markings

Emanuele Petrilli

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,是一个用小望远镜即可轻易找到的天体。在这张跨幅将近1度的影像里,距离约5,000光年远的三叶星云,与疏散星团M21(右)分享了这片取景佳妙的视野,形成了探索天体对比的彩色案例。被尘埃带割成三片的三叶星云,大小约为40光年,年龄只有300,000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。而距离和M20相当的疏散星团M21,内部恒星的年龄则是远较年长的8百万年。虽然它们分享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。

明日的图片: dark markings