Upside down rainbow

Last week we saw a circumzenithal arc, which is a somewhat rare natural phenomenon outside the polar regions. It was right overhead, surprisingly bright, and lasted ten minutes.

Explanation: the Sun is at an angle of about 22 degrees above the horizon. There are zillions of hexagonal ice crystals in the stratosphere. Sunlight hitting the ice crystals at 90 degrees goes through two internal reflections, and sends a rainbow earthwards.

Leave a comment if you have seen one of these.Read more at http://www.cambridge-news.co.uk/cn_news_home/DisplayArticle.asp?ID=349778

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