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>> Weatherweb Reporters << Circumzenithal Arc An upside-down rainbow… Really? By Garry Nicholson in Darley Dale, Derbys 00:00hrs 11/06/2012 Temperature: 13.5 Weather: Clear I was lucky enough to spot and photo what looked like an upside-down rainbow this weekend. No, I’m not talking rubbish, what I saw was a relatively unusual halo phenomena, referred to as a ‘circumzenithal arc’. A halo can become visible when the sun shines through thin high level cirrus-form cloud, formed of ice crystals. These wispy clouds do not block out much sunlight, but the tiny ice crystals cause refraction of the light through their flat hexagonal shape. Whilst the sun is high in the sky, a halo appears as a ring around the sun, and sometimes shows faint rainbow colours. However, the circumzenithal arc can only be viewed when the sun is lower in the sky, less than 30 degrees above the horizon. When individual ice crystals are aligned horizontally, the sunlight shines into the top of the crystal and is refracted out of the side, forming an arc of rainbow colours roughly 45 degrees above the sun, so almost directly overhead. So the next time you see faint wispy clouds in the sky, firstly (and carefully!) look out for a halo as a ring around the sun. If it is nearer sunset, then look straight up and you may spot this striking feature in the sky! >> Comments on this story << >> Add your comments below << Your name Email (not shown in posting): Location: Your comment): Security question: What colour is the sky? (the answer is blue but remove the 's)	>> Latest comments on this musing << [Scroll down to add your comment and see what others say] >> More from Weatherweb Reporters << Lords Test Match Forecast – Eng v NZ By Garry Nicholson in Edgbaston,Birmingham 17:00 15/05/13 First home test of the summer begins Recap of April 2013 By Garry Nicholson in Darley Dale, Derbys 14:30 02/05/2013 A pretty quiet month, cold start, mainly dry in Mids & South Masters Golf Forecast By Garry Nicholson in Darley Dale, Derbys 13:00 10/04/2013 Early thunderstorm threat, but a fine weekend [click here for a full list of Weatherweb Reporters stories] >> Simon's Weather Musings << Unseasonal Europe last week - warm east By Simon Keeling in Wombourne, Staffs 09:00 20/05/13 Not so good in the north west Texas tornadoes - six feared dead By Simon Keeling in Wombourne, Staffs 16:45 16/05/2013 Granbury tornado video [click here for a full list of Simon's weather musings] >> Captain Bob's Dispatches << Seasonal Outlook By Captain Bob in Kingswinford 11:00 19/05/2013 July looks best Month Ahead By Captain Bob in Kingswinford 10:00 19/05/2013 Weather machine games [click here for a full list of Simon's weather musings] >> Around the webcams << Latest webcam pics (add yours) >> Learning channel << Summer 2013 - Latest guidance >> Forecast channel videos << Wednesday's Look Ahead Tuesday's Look Ahead Monday's Look Ahead - Still confusion reigns! Sunday's Look Ahead - Hands up! 19/5/13 Saturday's Look Ahead video - Good news?