2021年08月30日:美国．西维吉尼亚州上空的火彩虹-（A Fire Rainbow over West Virginia）--原图下载
Image Credit: Christa Harbig
说明: 这朵云怎么啦？它是远处卷云里的冰晶，行为像漂浮的小三稜镜所产生的景观。这种景观因形似火焰而有火彩虹的称号，较文邹邹的名称则为平行于地平线的日承 (circumhorizon arc)。要看到日承，太阳在天空的仰角必须大于58 度，而且它的下方一定要有卷云，在此例里为纤维状卷云。此时，卷云里难以数计的扁平六角形冰晶必须平行于地表排列，才能以相似的模式共同折射阳光。因此，火彩虹算是很罕见。上面这幅记录火彩虹的主题影像，是在这个月稍早摄于美国．西维吉尼亚州的北福克山脉附近
原文：
Image Credit: Christa Harbig
Explanation: What's happening to this cloud?Ice crystals in a distant cirrus cloud are acting like little floating prisms. Known informally as a fire rainbow for its flame-like appearance, a circumhorizon arc appears parallel to the horizon.For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds present below -- in this case cirrus fibrates. The numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontalarcs are somewhat unusual to see. The featured fire rainbow was photographed earlier this month near North Fork Mountain in West Virginia, USA.
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