雪树上空的月晕

2021年02月01日

Lunar Halo over Snowy Trees
Image Credit & Copyright: Göran Strand

Explanation: Have you ever seen a halo around the Moon? This fairly common sight occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky. Each ice crystal acts like a miniature lens. Because most of the crystals have a similar elongated hexagonal shape, light entering one crystal face and exiting through the opposing face refracts 22 degrees, which corresponds to the radius of the Moon Halo. A similar Sun Halo may be visible during the day. Exactly how ice-crystals form in clouds remains a topic of research. In the featured image taken last week from Östersund, Sweden, a complete lunar halo was captured over snowy trees and rabbit tracks.

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Tomorrow’s picture: meteor streak and drift

雪树上空的月晕
影像提供与版权：Göran Strand

说明：你看过月亮周围的晕环吗？这种相当常见的景观之所以会发生，是因为几乎覆盖整个天空的高空薄云里，有数以百万计的小冰晶，而每个冰晶的功能都像是一个微小的透镜。因为大多数的这些冰晶形似颀长的六面体，光从一个晶面进入然后从对面穿出，发生22度角的折射，正好是月晕的半径。在白天，有时也会见到类似的日晕。然而，在云内冰晶到底是如何形成的，目前仍是研究的课题。在这张上星期摄于瑞典．厄斯特松德镇的主题影像里，有道完整的月晕高悬在地面雪树和兔子足迹的上空。

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明日的图片：meteor streak and drift