Copyright:
Sergio Mont�far
(Planetario Ciudad de La Plata,
pna)
原文:
What are those colorful arcs in the sky? Like rainbows that are caused by rain, arcs of sunlight broken up into component colors can also result when ice crystals floating in Earth’s atmosphere act together as a gigantic prism. The top color arc is more typical as it is part of the 22 degree halo surrounding the Sun when hexagonal ice crystals refract sunlight between two of the six sides. More unusual, though, is the bottom color arc. Sometimes called a fire rainbow, this circumhorizon arc is also created by ice, not fire nor even rain. Here, a series of horizontal, thin, flat ice crystals in high cirrus clouds refract sunlight between the side and bottom faces toward the observer. These arcs only occur when the Sun is higher than 58 degrees above the horizon. The featured sky occurred to the northwest in the early afternoon last month over a street Diagonal of La Plata City, Buenos Aires, Argentina. Follow APOD on: Facebook, Google Plus, or Twitter
中文翻譯:
🌈 在天空中出現的那些五顏六色的弧形是什麼？這些色彩的弧形類似於因為降雨而形成的彩虹，但它們的形成是由於漂浮在地球大氣中的冰晶像一個巨大棱鏡一樣工作。上面的色彩弧是更常見的現象，它是環繞太陽的22度光環的一部分，當六邊形冰晶在兩個側面之間折射陽光時形成的。
然而，更不尋常的是下面的色彩弧。人們有時稱之為火彩虹（fire rainbow），這是俗稱的地平線弧（circumhorizon arc），同樣是由冰晶造成的，而不是火或雨。這裡，一系列橫向、薄平的冰晶在高空的卷雲中折射陽光，通過側面和底面朝向觀察者。這些弧形僅在太陽高於58度時出現。
這個天象上個月在阿根廷布宜諾斯艾利斯省拉普拉塔市的西北方於早午時分出現。
#天空奇觀 #火彩虹 #冰晶 #雷射色彩 #天文現象 #美麗的自然 #阿根廷 #拉普拉塔 #夢幻天空
來源:NASA每日圖片
