One of our readers noticed a ring around the sun from her balcony in Trondheim, central Norway. Is this common? Elisabeth Eidem asks. And what exactly is it?
"This is a light phenomenon that you can see fairly often if you pay attention," says Anders Doksæter Sivle. He is a meteorologist and researcher at the Norwegian Meteorological Institute.
The ring is called a halo and has been used as a sign of changing weather throughout history.
This is what the ring around the sun looked like from Elisabeth Eidem’s balcony.(Photo: Private)
Light hits tiny ice crystals
But what creates the ring?
Annonse
"A halo like this is almost always caused by a special type of cloud called cirrostratus," Sivle explains.
Cirrostratus clouds form a thin layer high in the atmosphere, typically around 5,000–10,000 metres above the ground.
Even in June, when Eidem saw the ring of light from her balcony, temperatures at that altitude would be below freezing.
As a result, these clouds do not contain liquid water. Instead, they are made up of ice crystals.
The light is split into the colours of the rainbow
When sunlight hits the ice crystals, something similar to what happens in a rainbow takes place, Sivle explains.
"Light contains all the colours of the rainbow. So when it hits an ice crystal, it's split into its individual colours," he says.
While a rainbow is caused by sunlight hitting water droplets lower down towards the ground, a halo is caused by sunlight hitting these high-altitude ice crystals.
"It isn't particularly easy to see the colours in a halo. But you may be able to see that it's red on the inside and violet on the outside," says Sivle.
Researcher Anders Doksæter Sivle at the Norwegian Meteorological Institute says it is possible to see a halo quite often – if you remember to look for one.(Photo: Vilde Jagland / MET)
Can predict bad weather
The light is refracted in such a way that the angle between the sun and the ring is approximately 22 degrees.
You can check this using your own hand, Sivle explains.
Stretch your arm straight out towards the sun and keep your fingers together. If your thumb is pointing directly at the sun, the solar halo should line up roughly with your little finger, according to the researcher.
And solar halos can actually provide a clue that rain or snow may soon be on the way.
That is because cirrostratus clouds are often the beginning of a weather front.
"It's a little more complicated than that, but it's a classic old weather sign. If you see a ring around the sun, you can expect precipitation within the next 12 hours," says Sivle.
Sun dogs and sun pillars
Ice crystals high up in the sky can also create other light phenomena. If there is little wind at high altitudes, for example, bright spots can appear on either side of the sun, known as sun dogs.
And around sunrise or sunset, ice crystals can refract the light so that sun pillars form above and below the sun.
Other types of particles can also create different light phenomena.
“When sunlight hits particles such as water, dust, and ice in the air, it produces different effects, such as rainbows, halos, or a whole range of oher phenomena,” the researcher says.
