A Parhelion, also known as mock suns or sun dogs, appear as two bright spots on either side of the Sun, creating the illusion of three suns in the sky.

Parhelia are the result of sunlight passing through hexagonal ice crystals contained within cirrus cloud. They often appear in conjunction with 22° Haloes which are produced under the same conditions.

Light refracts from hexagonal ice crystals from cirrus cloud or, during especially cold weather, ice crystals which have fallen to low levels - known as diamond dust. Similar to a prism, the crystals bend the Sun's light as it passes through them, with a minimum deflection of 22°.

In the right circumstances two sun dogs may appear with a slight colouration of red and blue. Sometimes only one will appear or one will be notably brighter than the other. Most often they will appear as two luminous areas either side of the Sun, with no discernible colour.

Although it is very rare, it is possible for an unusually bright moon to create the same effect.

Last updated: 5 August 2014