Explanation: Why would the sky glow like a giant repeating rainbow? Airglow. Now air glows all of the time, but it is usually hard to see. A disturbance however — like an approaching storm — may cause noticeable rippling in the Earth’s atmosphere. These gravity waves are oscillations in air analogous to those created when a rock is thrown in calm water. The long-duration exposure nearly along the vertical walls of airglow likely made the undulating structure particularly visible. OK, but where do the colors originate? The deep red glow likely originates from OH molecules about 87-kilometers high, excited by ultraviolet light from the Sun. The orange and green airglow is likely caused by sodium and oxygen atoms slightly higher up. The featured image was captured during a climb up Mount Pico in the Azores of Portugal. Ground lights originate from the island of Faial in the Atlantic Ocean. A spectacular sky is visible through this banded airglow, with the central band of our Milky Way Galaxy running up the image center, and M31, the Andromeda Galaxy, visible near the top left.
Tomorrow’s picture: infrared galactic center
说明: 为何天空会出现一道道像庞大彩虹的辉光？因为有气辉。其实地球大气一直都在散发辉光，只是通常难以察觉而已。不过，如果附近有雷暴系统这类的扰动，就会在地球大气中产生可见的波纹。这种空气中的重力波，酷似投石于平静水面所产生的涟漪。这张几乎是顺着气辉峰墙方向拍摄的影像，可能让这些波动结构变得特别的清晰。不过，它的色彩到底是怎么来的？暗红的气辉可能是来自85公里高处，受到太阳紫外光激发的羟基(OH)分子。橙色和绿色气辉，则可能是由更高之处的钠及氧原子所发出。这幅主题影像，是在攀登 葡萄牙亚速尔群岛的皮可山之时所拍摄。地面的灯火，来自座落于大西洋里的法亚尔岛。在这些带状气辉后方的精采天空中，有向上伸展的银河系盘面，以及位在影像上左方的仙女大星系M31。
明日的图片: infrared galactic center