Sun and ice combine to make nice

A sun pillar caused by sunlight reflecting off plate-shaped ice crystals looks like a laser beam at sunrise on Feb. 17, 2013. Credit: Jim Schaff

Sometimes readers will send in photos of especially beautiful sky phenomena. I’m grateful when they do because then I can share them with you. Jim Schaff of Duluth has a home on the crest of a hill which gives him a decided advantage in photographing sunrises. Two days ago he grabbed his camera to take this superb image of a sun pillar.

Sun pillars form when sunlight reflects off the bottom surfaces of ice crystals shaped like hexagonal bathroom tiles. When they hover with their horizontal surfaces parallel to the ground, sunlight reflects from them like a billion tiny mirrors. Voila! A column of light forms. The phenomenon is best viewed near sunrise and sunset on cold mornings. Often you can’t even see the crystals, but the pillar tells us they’re there all the same.

A double halo, dual sundogs and an upper Parry Arc dress up a sunrise late last month. Credit: Sparky Stensaas

We’ve had lots of cold weather in my part of the country this February. Sparky Stensaas, another Duluthian, took this photo of all kinds of crystal cool things happening around the sun. Let’s do some dissecting and examine each one:

* Sun pillar – the spike of light sticking up from the sun
* The smaller halo is the common 22-degree variety and caused by light refracted or bent through billions of randomly-oriented, hexagonal ice crystals shaped like stubby pencils.
* Sundogs – the halo is flanked by two bright sundogs, so-named because they accompany the sun. They’re formed by light refracting through hexagonal, plate-shaped crystals, the broad sides of which are parallel to the ground.

So you can picture them more easily, these are the two basic kinds of ice crystals we’re talking about.

* 46-degree halo – this larger ring is much rarer than the 22-degree halo and forms when light passes through the side faces of randomly oriented, pencil-shaped crystals.
* Upper tangent arc - Light passing through a side faces of pencil crystals with their long sides parallel to the ground creates the bright spot atop the smaller halo.
* Parhelic circle – Look closely and you’ll see a faint arc passing through the sundogs and continuing beyond. This unusual phenomenon happens when light is reflected mirror-like from the vertical faces of several different varieties of ice crystals.

The sun shines in a clear avenue between streamlined bands of altocumulus clouds above the Great Lakes Aquarium in Duluth this morning. Photo: Bob King

Wow! You just never know what the sun and clouds will be up to next. Just today I was driving home from a photo assignment for my newspaper and saw the sun shining between banks of smooth altocumulus clouds. While there was little in the way of crystal displays, the streamlined aspect of the clouds highlighted by the sun was beautiful to see.

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