2020 March 18
Anticrepuscular Rays over Florida
Image Credit & Copyright: Bryan Goff
Explanation: What’s happening behind those clouds? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a Sun setting on the other side of the sky. Pictured here are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds. Now although sunlight indeed travels along straight lines, the projections of these lines onto the spherical sky are great circles. Therefore, the crepuscular rays from a setting (or rising) sun will appear to re-converge on the other side of the sky. At the anti-solar point 180 degrees around from the Sun, they are referred to as anticrepuscular rays. Featured here is a particularly striking display of anticrepuscular rays photographed in 2016 over Dry Tortugas National Park in Florida, USA.
Tomorrow’s picture: open space
美國佛羅里達州上空的反雲隙光
影像版權與提供: Bryan Goff
說明: 這片雲的後方到底發生了什麼事？ 雖然這幅景觀看來有些超自然，不過它只是落日在那端天空造成的效應而已。 這種現象稱為反雲隙光。 要了解這種現象，讓我們從白畫時，陽光穿過雲隙所形成的平常雲隙光開始說吧。 雖然這些透過雲隙的陽光的確是沿著直線前進，不過當它們投射到球狀的天空後，就成為一個個大圓。 也因此，來自落日或旭日的雲隙光，視覺上會在反方向重聚起來。 而這種重聚在和太陽相隔180度反日點的光線，就稱為反雲隙光。 這幅特別精采的反雲隙光景觀，是在2016年攝於美國． 佛羅里達州． 海龜國家公園的上空。
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