Astronomy Picture of the Day——横跨南冕座
Across Corona Australis
Image Credit & Copyright: Fabian Neyer
Explanation: Cosmic dust clouds are drapedacross a rich field of stars in this broad telescopic panorama near thenorthern boundary of Corona Australis, the Southern Crown. Less than 500light-years away the denser clouds effectively block light from more distantbackground stars in the Milky Way. The entire vista spans about 5 degrees ornearly 45 light-years at the clouds' estimated distance. Toward the right liesa group of bluish reflection nebulae cataloged as NGC 6726, 6727, 6729 and IC4812. The characteristic blue color is produced as light from hot stars isreflected by the cosmic dust. The dust also obscures from view stars in theregion still in the process of formation. Smaller yellowish nebula NGC 6729surrounds young variable star R Coronae Australis. Below it are arcs and loopsidentified as Herbig Haro (HH) objects associated with energetic newborn stars.Magnificent globular star cluster NGC 6723 is above and right of the nebulae.Though NGC 6723 appears to be part of the group, its ancient stars actually lienearly 30,000 light-years away, far beyond the young stars of the Corona Australisdust clouds.
横跨南冕座
这幅广阔的望远镜全景照片呈现出南冕座北缘附近、交织着富饶恒星的宇宙尘埃云。这些致密的尘埃云距离地球不到500光年，几乎完全遮挡住了银河中更遥远的恒星星光。以该星云的距离估算，这整幅照片覆盖了5度，相当于将近45光年的天区。照片右侧是一群蓝色反射星云，编录号分别为NGC 6726、6727、6729和IC 4812。它们呈现的蓝光是炽热恒星的星光受到宇宙尘埃反射所致。而这些尘埃还遮挡住了该区域内仍在形成过程中的恒星。较小的淡黄色星云NGC 6729围绕着年轻变星南冕座R星。它下方的弧状和环状结构被认为是与活跃新生恒星有关的赫比格-哈罗天体。壮美的球状星团NGC 6723位于该星云右上方，尽管它看上去好像是这群星云的一分子，但它内部古老的恒星实际上距离地球将近3万光年，远远超过了南冕座尘埃云年轻恒星离我们的距离。
参考文献：
https://apod.nasa.gov/apod/image/1811/coronaAustralis_l1500.jpg
近期文章：
Astronomy Picture of the Day——从南十字星到海山二星