Sundog

On October 23, 2011 · 4 Comments

I mentioned Goldfield, Nevada recently. I noticed a street called Sundog Avenue that looked like the kind of place where one could experience a sundog in person. I tucked the thought away for a few days until I had more time to explore it.

A sundog describes a specific atmospheric condition that allows a bright spot of light to appear on both sides of the sun. Sometimes it’s called a mock sun. Scientifically it’s a parhelion which derives from the Greek, “beside the sun.” Maybe it’s easier to demonstrate it in a photograph.


Sundogs and 22 degree Halo
SOURCE: flicker, Creative Commons – "Attribution-NonCommercial-ShareAlike 2.0 Generic (CC BY-NC-SA 2.0)"

This image that I borrowed from flickr has sundogs — the two bright spots — plus a halo. No wonder these phenomena were sometimes mistaken for omens or signs from God in earlier times. They’re pretty freaky. The Weather World 2010 Project provides a succinct explanation:

Sundogs form as sunlight is refracted by hexagonal plate-like ice crystals with diameters larger than 30 micrometers and their flat faces horizontally oriented. Sundogs are visible when the sun is near the horizon and on the same horizontal plane as the observer and the ice crystals. As sunlight passes through the ice crystals, it is bent by 22 degrees before reaching our eyes, much like what happens with 22 degree halos. This bending of light results in the formation of a sundog. The difference between sundogs and halos is the preferential orientation of the ice crystals through which the light passes before reaching our eyes. If the hexagonal crystals are oriented with their flat faces horizontal, a sundog is observed. If the hexagonal crystals are randomly oriented, a halo is observed.

I understand the term parhelion because it makes perfect sense. The etymology of sundog is a bit more shrouded in mystery. Most sources don’t seem to know much more than it’s "obscure." I did find a book published all the way back in 1882 that took a stab at it though. According to Folk-etymology: A Dictionary of Verbal Corruptions…, it’s "the phenomenon of false suns which sometimes attend or dog the true when seen through a mist… dog here is no doubt the same word as dag, dew or mist." OK, if you say so, Mr. Folk-etymology Dictionary. I have no means to confirm that interpretation so feel free to accept or reject that claim, or even create one of your own.

Google Street View may have also captured a sundog in the United Kingdom.


Sundog Outside of London

I wish I could take credit for this find but it’s not mine. It comes from a flickr discussion group on sundogs and related phenomena. I took a screen grab because it will disappear the next time Google refreshes its imagery outside of London. It’s still there as of October 2011 when I published this post if you wish to ponder it further.



View Larger Map

Curiosity got the best of me so I decided to see if I could find any sundog place names, discovering positive results in the US Board of Geographic Names database and Natural Resources Canada – Geographical Names Canada database. The pickings were slim. I also looked in Australia and the UK where I found nothing.



View Larger Map

I had much better luck finding streets named after sundogs. I’m sure there are many others because I found these without too much difficulty and I stopped when I got tired of searching. These tend to be located in wide-open spaces where sundogs would be easier to spot, as one would expec

On October 23, 2011 · 4 Comments

4 Responses to “Sundog”

  1. Corey Loney says:

    No geographical features, but I’ve observed sundogs numerous times in Northern Virginia. On winter days where there are high clouds, driving west from the Beltway on Braddock Rd. late in the day seems to increase one’s chances of seeing sundogs considerably, though I don’t know why. During the winter of the Snowpocalypse, I saw them from there on three or four different occasions.

  2. stangetz says:

    They happen quite often and all over the place. Most people dont realize they are there because you dont necessarily want to look at the sun, even though these are off to the side. Alos, having polarized sunglasses on helps.

  3. Bill Harris says:

    FYI, typo in the second line- “could”

    I’ve seen a fair number of sundogs here in Delaware. I can’t say how many times I’ve seen them- enough times to not be surprised but not enough times to not stop and admire them. Like Corey Loney’s experiences, they seem to occur in the winter when there are high clouds in the sky. That makes sense, as those are ideal conditions for ice crystals in the atmosphere.

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