瑞典上空的日晕
Sun Halo over Sweden
Video Credit & Copyright: Håkan Hammar (Vemdalen Ski Resort, SkiStar)
Explanation: What’s happened to the Sun? Sometimes it looks like the Sun is being viewed through a giant lens. In the featured video, however, there are actually millions of tiny lenses: ice crystals. Water may freeze in the atmosphere into small, flat, six-sided, ice crystals. As these crystals flutter to the ground, much time is spent with their faces flat and parallel to the ground. An observer may find themselves in the same plane as many of the falling ice crystals near sunrise or sunset. During this alignment, each crystal can act like a miniature lens, refracting sunlight into our view and creating phenomena like parhelia, the technical term for sundogs. The featured video was taken in late 2017 on the side of a ski hill at the Vemdalen Ski Resort in central Sweden. Visible in the center is the most direct image of the Sun, while two bright sundogs glow prominently from both the left and the right. Also visible is the bright 22 degree halo — as well as the rarer and much fainter 46 degree halo — also created by sunlight refracting through atmospheric ice crystals.
Tomorrow’s picture: giant storms
瑞典上空的日晕
影片提供与版权: Håkan Hammar (Vemdalen Ski Resort, SkiStar)
说明: 太阳发生了什么事？有时候，我们好像是透过一个巨大的透镜在看太阳。而在这部主题影片里，事实上是透过数百万个微小的冰晶透镜看太阳。大气的水结冰时，有时会形成细小扁平的六边形冰晶。这些冰晶飘落到地面的过程中，大部份的时候扁平面会和地面平行。在日出或日落时，如果观察者的视线恰好穿过由许多冰晶所形成的平面，此时每个冰晶的作用就像是一个微小的透镜，把阳光折射到我们的眼睛里，造成了幻日的现象。这部主题影片，是2017年底在瑞典斯德哥尔摩Vemdalen滑雪渡假村的一座雪丘边坡拍摄的。在影片直视太阳的片断，可见到太阳的左方及右方，各有一个醒目明亮的幻日。此外，影片中也可以见到张角22度的日晕，以及同样是大气冰晶折射阳光所造成的、较罕见也较暗的46度日晕。 (幻日俗称为sundog，学名为parhelia)
明日的图片: giant storms
