WHAT IS A SUNDOG?

Sundogs or parhelia are seen over a snow-covered field in Duluth. Sundogs, also known as mock suns because of the bright spots at either side of the sun, appear when light from the sun near the horizon is refracted by ice crystals in the atmosphere

The sight of three suns in the sky is enough to make most of us rub our eyes in disbelief, but centuries ago, the strange sight was seen as a bad omen. 

The unusual spectacle is called a parhelion or a sundog.

It is the result of a natural phenomenon in which sunlight passes though snow crystals in a particular way when they are suspended in the air.

Sundogs are created when sunlight is refracted by large, hexagonal ice crystals, such as those in snowflakes. 

They typically appear as two coloured patches of light either side of the sun and though rare, can in theory be seen anywhere in the world in any season.

They are created by the refraction of light passing through flat, hexagonal ice crystals in high, cold clouds.

The crystals act like prisms so that as light passes through them, it is bent by exactly 22 degrees before reaching viewers' eyes to make the illusion.

If the crystals are more randomly located in clouds, a complete ring around the sun is visible, called a halo.

Pictured is the moon halo over the, Isle of Wight. The moon halo is formed by a high-altitude ice crystal cloud that gathers around the moon

But if the crystals sink through the air, they become arranged in vertical lines, so that the sunlight is refracted horizontally, to make sundogs, as seen in these images.

If the phenomenon is seen as the sun is rising, the sundogs gradually move further away from the sun, but always stay at the same elevation, so the three 'orbs' appear to be the same distance from the horizon.

They are reddest in colour when they are near to the sun and fade to yellow, orange and then blue as they move away. The colours of sundogs merge into a white halo in some instances.