A series of rare shining arcs and halos of light surrounding the sun were seen in the sky above the UK recently.
The phenomena, which included a halo, a sundog, and a complete parhelic circle, were captured in photos by Alan Fitzsimmons, an astronomer at Queen’s University Belfast. The display lasted around 30 minutes, Fitzsimmons told Live Science.
The scientist’s image includes a 22-degree halo, the large circle surrounding the sun; a pair of ‘sundogs’, the bright points on each side of the 22-degree halo; and a complete parhelic circle, the line that bisects the circle, while also encircling the entire sky.
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The halo appears as a large, white ring around the sun, while a sundog is a bright spot that appears on either side of the sun. Both are caused by the refraction of sunlight through ice crystals in the atmosphere.
A full parhelic circle, also known as ‘sun rings’ or ‘ice rings’, is rare because it requires at least five internal reflections from millions of individual ice crystals, all catching sunbeams simultaneously, according to Spaceweather.com.
They are most likely to be seen in high-latitude regions, such as the Arctic and Antarctic, making them a precious sight in the UK.
The combination of these three phenomena is extremely rare. Fitzsimmons said that he had only seen it once before, in 2015. The phenomena were seen across much of the United Kingdom, but they were particularly visible in Northern Ireland.
The combination of these three phenomena is extremely rare because it requires specific conditions to be met. The ice crystals that cause these phenomena must be perfectly aligned, and the sunlight must be refracted at just the right angle.
The parhelic circle is the rarest and most ‘impressive feature’ in the image, while the others are fairly common, according to Fitzsimmons.
‘The sun can be quite bright when they [the phenomena] are visible, so to notice them, you need to block out the sun with your thumb or a tree,’ Fitzsimmons said. ‘But anytime it’s sunny with high-altitude wispy clouds, it’s worth taking a look to see if there is a halo or maybe something more.’
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