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“Heart of the Matter,” Nature Version

Heart of the matter

We’ve had particularly cold temperatures in Minnesota so far this winter season. Back in December conditions were such that “sun dogs” appeared.  A sun dog (scientific term, parhelion from Greek parēlion, meaning “beside the sun”) is an atmospheric phenomenon that creates bright spots of light in the sky, often generating a luminous ring or halo on either side of the sun. They may appear as a colored patch of light to either side of the sun and can be seen anywhere in the world during any season. Sun dogs are not always obvious or bright and are best seen and most conspicuous when the sun is low.

My understanding is that sun dogs are commonly made by the refraction of light from ice crystals in high and cold cirrus clouds and are most likely to be spotted during very cold weather. The ice crystals, called diamond dust, drift in the air at low levels and act as prisms. The crystals can be randomly oriented and actually cause a complete ring…halo…around the sun. More often, as the crystals sink through the air, they become vertically aligned, so sunlight is refracted horizontally; in this case, sun dogs appear.

Some say it is possible to predict the forms of sun dogs as would be seen on other planets and moons. Mars might have sun dogs formed by both water-ice and CO2-ice. On the giant gas planets — Jupiter, Saturn, Uranus and Neptune — other crystals form the clouds of ammonia, methane and other substances that can produce halos with four or more sun dogs.

Talk about getting to the heart of the matter; a picture is really worth 1,000 words!

Source:  Wikipedia http://en.wikipedia.org/wiki/Sun_dog

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