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| A 22° Halo looms over a stone ship an HDR tonemapped image by M�ns Hagberg. ©Måns Hagberg, shown with permission. The ship is a two and a half thousand year old late Bronze Age funeral monument at Fröjel, Gotland, Sweden. The tone mapping reveals well the darker sky inside the 22 degree halo. The halo formed by poorly oriented ice crystals of an uncertain kind is not a 'ring'. The halo light starts, and is most intense, some 22° from the sun and extends outwards to 50°. The inner limit of 22° is the minimum angle that light is deviated when passing through an ice crystal with entrance and exit faces inclined at 60°. Sunlight cannot be deflected through a smaller angle and consequently there is a dark 'hole in the sky' where no ice crystals glint. Alexander's Dark Band between rainbows is similarly produced. |
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