Unusual flat rainbow dazzles Mossel Bay

Posted by Ilhaam Bardien on 6 April 2020

On 6 April, a Mossel Bay resident was lucky enough to catch a glimpse of what appeared to be a flat rainbow. What emerged was a stunning image of a rainbow like we’ve never seen before.

Amanda Walden, the resident who captured the image was unsure of why it was not arched. She took to Facebook to see if she could find out.

‘I photographed this ‘flat rainbow’ earlier today from my home in Danabay (Mosselbay). A cold front is moving through the area. Could somebody please explain why it isn’t arched like ‘normal’ rainbows?’ she said in her post.

Image: Facebook / Amanda Walden

 

Rainbows are formed when beams of light hit droplets of water and bend as they enter. The light reflects off the back of the droplet and leaves through the front, back towards the viewer of the rainbow. Red light bends the most and violet bends the least.

Every colour bends through a certain angle. Red light is reflected back at 42 degrees away from its original direction and blue light bends 40 degrees. This means that every colour shows up in a different position in the sky (for example, red will show up at every area in the sky which is 42 degrees away from a theoretical line that connects the sun to the rainbow viewers head).

Together, these placements in the sky form the arch of a rainbow.

Explaining why this specific rainbow was not arched, another Facebook user, Willem Viljoen commented. ‘It’s not actually a rainbow at all. That looks like a circumhorizontal arc, a related but different optical phenomenon. You’re very lucky to have caught a full one like that, they are generally patchy. It’s usually caused by transparent high altitude clouds or suspended ice particles in the air,’ he said.

The Naked Scientists, who answer common questions online claim that ‘if the sun is high in the sky, you just see the top of the circle and the rainbow looks flat’.

Whatever the reason for this flat rainbow, it definitely was a sight to see!

Image: Facebook / Amanda Walden






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