夜光云、倒影与剪影

2019 June 26

夜光云、倒影与剪影
影像来源与版权: Peter Simmering

说明：有时候地面上是夜晚，但天空中是白天。当地球自转遮挡了太阳时，日落便从地面升起。因此，在地面上的日落时分，阳光仍然照耀着天空中的云层。在通常情况下，我们可以看到美丽的落日，但不同寻常的夜光云漂浮得如此之高，以至于在天黑后还能看到。夜光云通常太过黯淡而不会被人们看到，它们可能在夏季日落之后、当阳光从下方照耀时，才能显现出来。夜光云是已知最高的云层，它被认为是极地中间层云的一部分。这幅特征影像拍摄于两周之前，它呈现了荷兰.兹沃勒市北部遥远天空中的网状夜光云和一片小湖中的夜光云倒影，以及地平线上显著的树木剪影。这种异常明亮的夜光云不断出现在北欧的大部分地区。关于夜光云的多数发现都来自于过去十年，而它们是如何形成和演化的仍然是一个有待积极研究的课题。

Noctilucent Clouds, Reflections, and Silhouettes
Image Credit & Copyright: Peter Simmering

Explanation: Sometimes it’s night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above. Under usual circumstances, a pretty sunset might be visible, but unusual noctilucent clouds float so high up they can be seen well after dark. Normally too dim to be seen, they may become visible just after sunset during the summer when illuminated by sunlight from below. Noctilucent clouds are the highest clouds known and thought to be part of polar mesospheric clouds. Featured here as they appeared two weeks ago, a network of noctilucent clouds was captured not only in the distant sky but in reflection from a small lake just north of Zwolle, Netherlands, with trees in stark silhouette across the horizon. Unusually bright noctilucent clouds continue to appear over much of northern Europe. Much about noctilucent clouds has been discovered only over the past decade, while how they form and evolve remains a topic of active research.