2025年8月22日
A Tale of Two Nebulae
Image Credit & Copyright: Kent Biggs
Explanation: This colorful telescopic view towards the musical northern constellation Lyra reveals the faint outer halos and brighter central ring-shaped region of M57, popularly known as the Ring Nebula. To modern astronomers M57 is a well-known planetary nebula. With a central ring about one light-year across, M57 is definitely not a planet though, but the gaseous shroud of one of the Milky Way’s dying sun-like stars. Roughly the same apparent size as M57, the fainter and more often overlooked barred spiral galaxy at the left is IC 1296. In fact, over 100 years ago IC 1296 would have been known as a spiral nebula. By chance the pair are in the same field of view, and while they appear to have similar sizes they are actually very far apart. At a distance of a mere 2,000 light-years M57 is well within our own Milky Way galaxy. Extragalactic IC 1296 (aka PGC62532) is more like 200,000,000 light-years distant. That’s about 100,000 times farther away than M57 but since they appear roughly similar in size, former spiral nebula IC 1296 must also be about 100,000 times larger than planetary nebula M57. Look closely at the sharp 21st century astroimage to spot even more distant background galaxies scattered through the frame.
Tomorrow’s picture: light-weekend
双星云记
影像提供与版权: Kent Biggs
说明: 这幅色彩缤纷的望远镜影像展示了北天星座「天琴座」（Lyra）M57 —— 也就是人们熟知的「环状星云」（Ring Nebula）。在影像中，可以看到昏暗的外层晕环与明亮的中央环状结构。对现代天文学家而言，M57是一个典型的「行星状星云」。然而，它与行星并无关联，而是银河系中一颗类太阳恒星在生命末期所抛出的气体外壳。其中央环状结构直径约为一光年。在M57左侧，可以看到另一个常被忽略的天体——棒旋星系IC 1296。事实上，在一百多年前，IC 1296曾被称作「螺旋星云」。这两个天体恰巧位于同一视场，虽然在影像中大小相仿，但距离却有天壤之别。M57位于距离地球仅约2,000光年的银河系内，而河外星系（又名PGC 62532）则遥远至约2亿光年之外，足足远上10万倍。由于在影像中两者看似大小相近，这意味着IC 1296的真实尺寸也必然比M57大上约10万倍。在这张高解析度的21世纪天文影像中，若仔细观察，还能发现背景中散布的更多遥远星系。
明日的图片: light-weekend
