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.