Mahmut Karacan saw this at Diyarbakir, Turkey. “It was an amazing day. First black clouds appeared like an apocalypse. After that lightning with rain. Then we had this red rainbow.”?The bow is almost semicircular because the sun is near to setting. When the sun is low, bows are high. Sunset rays have a long path through the atmosphere and are highly reddened due to blue light being preferentially scattered away by air molecules and fine dust/aerosol.?But why a red disk? All rainbows are disks. We notice a bow’s disk more when - like here - its colour contrasts with the sky. When the sun is higher the disk is white and then shows up as brighter sky inside the bow.
         
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