Sundog!

Some thought they predicted the death of kings.  

Before the Battle of Mortimer's Cross in 1461, the future King Edward IV tried to convince his troops, frightened by the appearance of three suns, that they represented the Holy Trinity and presaged a great victory.  (He won).

And during the past days several of you have seen this apparition here in the Northwest and sent me pictures and questions.

What am I talking about?   Sundogs.  Also known as mock suns or parhelia.

To begin, here are two pictures sent to me today by Lief Zimmerman (the second a blow-up of a portion of the first)

And here is a dramatic example in which the sun and two "dogs" are clearly visible.

The two sundogs, or mock suns, frequently show a rainbow-like effect and often appear as brighter spots in a partial or total halo around the sun.

Why do sundogs exist?

Sundogs are the result of the refraction of light through ice crystals, normally ice crystal clouds such as cirrostratus or cirrus.    Light from the sun is bent or refracted by the ice crystals, which are six sided (or hexagonal).  The sun's rays are generally bent by 22 degrees when they goes through the ice crystal from one side to the other.   If the ice crystals are randomly oriented one sees a halo around the sun.   But if the ice crystals are shaped in plates, they tend to orient themselves in one way (wide side up and down).  The result is then a partial halo, with two "suns" on both sides (see schematic).

Why the rainbow colors?   Turns out that the ice crystals can act like little prisms since the bending of light (refraction) depends on the wavelength of light.  This causes a split of the sun's ray into various wavelengths or colors, a process known as dispersion (see schematic below).

Why don't we get sundogs all the time?.  Well, first you need sun (a relative rarity in these parts).  Then you need ice crystal clouds in which the shapes of the ice crystal are right (the relative flat plates shown above).  That requires that the crystals form in  a certain temperature change.  Then you need the right geometry of the sun relative to the clouds.  I probably see sun dogs around here 3-8 times a year...not rare, but not an everyday affair.

Shakespeare wrote about sundogs at length, here is a portion from Henry IV, Part I:

EDWARD
Dazzle mine eyes, or do I see three suns?

RICHARD
Three glorious suns, each one a perfect sun;
Not separated with the racking clouds,
But sever'd in a pale clear-shining sky.
See, see! they join, embrace, and seem to kiss,
As if they vow'd some league inviolable:
Now are they but one lamp, one light, one sun.
In this the heaven figures some event.

EDWARD
'Tis wondrous strange, the like yet never heard of.
I think it cites us, brother, to the field,
That we, the sons of brave Plantagenet,
Each one already blazing by our meeds,
Should notwithstanding join our lights together
And over-shine the earth as this the world.
Whate'er it bodes, henceforward will I bear
Upon my target three fair-shining suns.

I wish I could write like that!  Whether sundogs have anything to do with longevity of kings or the propects on the field of battle, I will leave that to philosophers and writers.

 Want to help find out the effects of coal trains on the local environment?

Atmospheric Chemistry Professor Dan Jaffe is ready to begin a study on air pollution from trains, especially freight  and coal trains, in the Puget Sound region.   Several state and local agencies told him that this work needs to be done, but that it is too politically hot for them to fund.

Considering the importance of this work, Dr. Jaffe is going to depend on crowd funding to support this effort.  For more information and perhaps to help, please check out this website: 

https://www.microryza.com/projects/do-coal-and-diesel-trains-make-for-unhealthy-air