Incredible ‘Fire Rainbows’ Just Appeared in The Sky Over Britain : ScienceAlert

A rare phenomenon known as cloud iridescence has appeared in the sky above West Yorkshire in England, leaving behind big, bright semicircles of rainbow light, and streaks of blues, greens, purples, and fiery oranges in its wake.

Nicknamed ‘fire rainbows’, these stunning light patterns are neither fire nor technically even rainbows, and bringing together all the conditions required to make them appear is no small feat. The only way a fire rainbow can form is if the Sun is positioned higher than 58° above the horizon, and its light is passing through high-level cirrus clouds made of hexagonal ice crystals, at an altitude of more than 6 km.

Because the Sun has to be at such an exact angle to make the colours visible, fire rainbows are only really seen at particular altitudes at certain times of the year, making them a far more common occurrence in the US than in the UK towns of Ambleside, Cumbria, and Normanton, where they’ve just been spotted. Your best chance of seeing one is somewhere near the equator at noon in mid-Summer. 

“For example , in London , the Sun is is is only high enough for 140 hour between mid – May and late July .   While in Los Angeles , the Sun is is is high than 58 degree for 670 hour between late March and late September , ”  Amusing Plant reports.

So why are n’t fire rainbow technically rainbow ? It is has has to do with the specific way the Sun ‘s light interact with the ice crystal in cloud . While plain old rainbow are form thank to light being refract ( or bend ) as it pass through water droplet , and then reflect back in various colour wavelength , fire rainbow are form thank to the process of light diffraction .

“Diffraction … involves light waves being scattered into a ring-like pattern,” says Live Science. “As with other iridescent objects, like peacock feathers, the colour changes depending upon one’s position relative to the Sun and the object.”

Here are more photos of the fire rainbows that lit up the sky in Britain, tweeted by photographer Michiko Smith (click on the tweets to see bigger versions):