Incredible scene spotted above Aussie town: 'That's amazing'

Despite looking similar to the recognisable rainbow, there is one key difference responsible for this optical phenomenon.

Residents in the NSW Northern Rivers were struck by a second rare weather spectacle this week after a rainbow-coloured cloud adorned the sky on Friday.

Pictures of the "optical phenomenon" were posted on Facebook by a local who couldn't believe the quality of the images despite only using his iPhone, describing the sight as being incredibly "pretty".

"How cool is this!" the man said.

Picture of the Circumhorizontal Arc.
The Circumhorizontal Arc was spotted by a local resident in Skennars Head who immediately stopped to snap a picture at his home. Source: Facebook / Weather Obsessed

The spectacle, known as a Circumhorizontal Arc, was likened to a multi-coloured feather as well as a unicorn's mane as it stretched out over the sky, and was spotted days after a rare wave-shaped cloud known as a Kelvin-Helmholtz cloud was seen in the area.

"This is amazing!" one user wrote. "Wow, this is sensational," another said.

Ice crystals responsible for "spectacular" sight

Despite being spotted in the height of summer, surprisingly this phenomenon is caused by ice crystals says Martin Singh, Professor at the School of Earth, Atmosphere, and Environment at Monash University.

"Cirrus clouds are high in the atmosphere and are made of ice crystals. It's very cold and they're frozen," he told Yahoo News Australia. "The light from the sun hits them and it refracts inside them, and it comes out the other side in a spectrum like a prism."

The Circumhorizontal Arc has very distinct colours.
There are several different weather phenomenon that produce a rainbow but this is identified as a Circumhorizontal Arc due to well-distinct colours, Professor Martin Singh said. Source: Facebook / Weather Obsessed

The awe-inspiring sight is only made possible when these "very small, hexagon-shaped" ice crystals are caught by the sun's rays at a specific angle, and is more common when the sun is high in the sky during the middle of the day.

Despite having "similar physics" as a rainbow which refracts and reflects within a raindrop, this weather phenomenon is different as it occurs at an angle to the sun and involves clouds. Sightings are non-existent in places with high latitudes like Northern Europe and Antarctica.

"[It's] not that uncommon between Brisbane and Sydney, but [it] can still be quite spectacular," Professor Singh concluded.

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