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Double Halo

15 July 2016

At www.spaceweather.com (July 15th 2016) … it seems the big sun spot is not acive. It has a stable magnetic field and there is no chance of a flare over the next few days. Noctilucent clouds are the highest clouds in the atmosphere, forming at the edge of space some 80km above the surface of the earth. They are caused by wisps of water vapour that wrap themselves around the smoke of incoming meteors. There are therefore lots of meteors interacting with the upper atmosphere – especially at this time of year. The resulting ice crystals glow electric blue in the night sky. To observe them (on a clear night of course) look west half an hour to one hour after sunset when the Sun has dipped minus 10 degrees below the horizon.

The image below was taken by Noel Keating in Co Donegal – a double sun halo. These too are caused by ice crystals but much lower in the atmosphere, forming in cirrus clouds 5 to 10 km above the surface. First we have the normal kind of halo at 22 degrees forming a ring around the Sun and then another circle crossing the Sun and hanging below it, known as a perhelic circle. The sky above Britain and Ireland on the 14th was full of ice crystals it would seem as there were many reports of halos.

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