埃特纳火山上空的光柱
Light Pillar over Volcanic Etna
Image Credit & Copyright: Giancarlo Tinè
Explanation: What happening above that volcano? Something very unusual — a volcanic light pillar. More typically, light pillars are caused by sunlight and so appear as a bright column that extends upward above a rising or setting Sun. Alternatively, other light pillars — some quite colorful — have been recorded above street and house lights. This light pillar, though, was illuminated by the red light emitted by the glowing magma of an erupting volcano. The volcano is Italy’s Mount Etna, and the featured image was captured with a single shot a few hours after sunset in mid-June. Freezing temperatures above the volcano’s ash cloud created ice-crystals either in cirrus clouds high above the volcano — or in condensed water vapor expelled by Mount Etna. These ice crystals — mostly flat toward the ground but fluttering — then reflected away light from the volcano’s caldera.
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埃特纳火山上空的光柱
影像提供与版权: Giancarlo Tinè
说明: 这座火山上空发生什么事？出现了极不寻常的火山光柱。一般常见的光柱，是因太阳而起，故多是在旭日或落日上空垂直上指的明亮光柱。天空也另有其他种类的光柱，有些甚至因街灯或住家灯火而起，而且色彩可极为缤纷。影像里的这道光柱，则是由爆发火山的红炽岩浆所投射。这座火山是意大利的埃特纳火山，记景的主题影像是摄于今年7月中旬某天落后数小时的单曝光照片。当时火山灰云上空的严寒，把高卷云或埃特纳峰喷出水汽冻结成冰晶。当这些扁平的冰晶缓缓飘落时，集体反射来自火山的破火山口之亮光，形成影像中的光柱。
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