[url=http://www.webphemera.com/2009/08/fire-rainbow.html]source[/url] [align=center][img]http://i47.tinypic.com/2qd7ddh.jpg[/img] If you are very lucky you may see a fire rainbow once or twice in your life. It sounds like it could be one of a series of children’s books – “Harry Potter and the Fire Rainbow” has a certain ring to it, but this phenomenon is not fiction. If you are in the right place and at the right time then a fire rainbow is something that you will remember witnessing forever. [img]http://i48.tinypic.com/vy173l.jpg[/img] To name it properly, a fire rainbow is a circumhorizontal arc. It is also known as a circumhorizon arc but whichever you chose, scientists (and aficionados) call it a CHA. It is given its name because it looks as if a rainbow has spontaneously combusted as it made its way across the sky. It could even be suspected, perhaps, that some malign fairy or goblin has blown the rainbow up to stop some errant human discovering that elusive pot of gold at its end! [img]http://i50.tinypic.com/bfo0eg.jpg[/img] The real explanation behind a fire rainbow lies more in science text books than in a Brothers Grimm tale. A CHA is a kind of halo – which is an optical phenomenon. These appear around the moon – or in this case the Sun. You have probably seen a halo yourself around a strong light source – take a look at street lights in the fog for example. [img]http://i50.tinypic.com/309u9uv.jpg[/img] [img]http://i48.tinypic.com/21epo9.jpg[/img] Although there are many different types of optical halos, a CHA is caused by the refraction though ice crystals in cirrus clouds of light from the sun. Refraction happens when the speed of light is reduced inside a particular medium. This particular refraction happens when light goes from air without cloud to air containing cloud. In this case it is vital that the cloud is cirrus in shape.[/align] [url=http://www.webphemera.com/2009/08/fire-rainbow.html]Read the rest of the article[/url]

Last edited by shana16 (2012-05-05 09:37:46)