What is a Sundog, and How Did “Sundogs” Get Their Name?

Friday, January 11, 2019 - 10:40am

I recently had someone send me a picture with a halo or rainbow around the sun. The person who sent the photo wanted to know what it was and what caused it to be there. I decided to spend a few moments today explaining what it was. Heres the image I got from the follower. 


The short answer is. It's a sun halo. Now for the longer version of what they are and why they are called sundogs & sun halo's.


What is a sundog?

A sundog is a concentrated patch of sunlight occasionally seen about 22° to the left or right of the Sun. Sundogs often form in pairs on either side of our daytime star when sunlight refracts through icy clouds containing hexagonal platecrystals aligned with their large, flat faces parallel to the ground. Technically known as parhelia (singular parhelion) they are often white but sometimes quite colorful, looking like detached pieces of rainbow, with red on the inside, toward the Sun, and blue on the outside.

A Sun halo, a circle of light that creates a circle 22° wide around the Sun, is a related phenomenon. As with sundogs, hexagonal ice crystals suspended in cirrostratus clouds refract sunlight to create the halo, sometimes also called an icebow, nimbus, or gloriole. Unlike sundogs, which generally only be seen when the Sun is near the horizon, the halo is visible even when the Sun is high. Sundogs appear along the 22° halo and disappear as the Sun rises.


Why are they called sundogs and sun halo's?

The exact etymology of sun dog largely remains a mystery. 

The phenomena of false suns which sometimes attend or dog the true when seen through the mist . A sun dog is a light spot near the sun, and water-dogs are the light watery clouds; dog here is no doubt the same word as dag, dew or mist.

Alternatively, Jonas Persson suggested that out of Norse mythology and archaic names — Danish: solhunde (sun dog), Norwegian: solhund (sun dog), Swedish: solvarg (sun wolf) — in the Scandinavian languages, constellations of two wolves hunting the Sun and the Moon, one after and one before, may be a possible origin for the term.

In the Anglo-Cornish dialect of Cornwall, United Kingdom, sun dogs are known as weather dogs (described as "a short segment of a rainbow seen on the horizon, foreshowing foul weather"). It is also known as a lagas in the sky which comes from the Cornish language term for the sun dog lagas awel meaning 'weather's eye' (lagas, 'eye' and awel, 'weather/wind'). This is in turn related to the Anglo-Cornish term cock's eye for a halo round the sun or the moon, also a portent of bad weather.

Regardless of how the names came about they are very cool to look at when you spot them in the sky. 

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