Let us start with the very basics today and go back to kindergarten! Don’t worry, what we will be discussing in the article is by no means kindergarten knowledge. There are 2 words that most of us learn during kindergarten: D for Dog and S for Sun. But did you know that using both these words together to make “Sundog” also makes perfect sense!

But, before we go into the details of what is a Sundog, let us look at the beautiful picture shared by a dear friend from Canada a few days ago. It is known as a Halo that happens when rays of the sunlight are bent (refracted) while travelling across thin sheets of hexagonal ice crystals present in the clouds. Known as Cirrostratus clouds, these clouds are usually formed at altitudes higher than at least 5km from the ground.  The light bends while traveling through the hexagonal ice crystals (hexagonal prisms) and creates a ring of white light that surrounds the sun and forms the Halo. Not just the sun, halos can also be formed around the moon under the right cloud conditions.

Now, coming back to the Sundog, it is an equally fascinating light phenomenon observed when most of the hexagonal crystals in the Cirrostratus clouds (mentioned above) are aligned along just one direction rather than at random. In such a case, the special geometrical conditions of the ice crystals (acting as aligned hexagonal prisms) and light bending (refraction) results in the formation of 2 bright spots besides the sun that are separated by 22°. Legend has it that the phenomenon gets its name of Sundog because the 2 bright spots of light follow the sun in a manner reminiscent of a dog following its master! Scientifically, the phenomenon has a more logical name of the parhelion (plural: parhelia), which originates from the Greek word parēlion meaning beside the sun. Detailed explanation of light refraction through the hexagonal prisms is beyond the scope of this article but for those of you who would like to understand it in more detail, make sure to check out this article.   

If you happen to be living in a cold place with clear blue skies, make sure that you check the skies for the Halos or the Sundog!