Astronomy Picture of the Day——天空的脉络
The Veins of Heaven
Image Credit & Copyright: P-M Hedén
Explanation: Transfusing sunlight through a still dark sky, this exceptional display of noctilucent clouds was captured earlier this month, reflected in the calm waters of Vallentuna Lake near Stockholm, Sweden. From the edge of space, about 80 kilometers above Earth's surface, the icy clouds themselves still reflect sunlight even though the Sun is below the horizon as seen from the ground. Usually spotted at high latitudes in summer months the night shining clouds have made a strong showing so far during the short northern summer nights. Also known as polar mesopheric clouds they are understood to form as water vapor driven into the cold upper atmosphere condenses on the fine dust particles supplied by disintegrating meteors or volcanic ash. NASA's AIM mission provides daily projections of noctilucent clouds as seen from space.
天空的脉络
本月早些时候，天空出现了异常的夜光云现象，阳光穿过寂静黑暗的天空，倒映在瑞典斯德哥尔摩附近的瓦尔伦图纳湖平静的水面上。从距离地球表面约80千米的太空边缘看，即使从地面看到的太阳位于地平线下方，冰云本身仍能反射阳光。夜光云通常出现在夏季的高纬度地区，到目前为止，它在北方短暂的夏夜里表现得非常抢眼。夜光云也被称为极地中层云，它被认为是进入寒冷高层大气的水蒸气凝结在由解体的流星或火山灰所产生的微细尘埃颗粒上而形成的。NASA的AIM任务提供了从太空看到的夜光云投影。
参考文献：
https://apod.nasa.gov/apod/image/1907/NLCReflectionsAPODheden.jpg
近期文章：
Astronomy Picture of the Day——天鹅座