Thursday, December 25, 2008

A Christmas Present from Nature

My sister, Joyce, and I were headed across State Route 741 near Lebanon, OH around 4:30 pm today and witnessed the most amazing sight. We noticed the clouds near the sun were lit up with color, blending from rich orange to yellow to a pale green and a hint of purple. It looked like a short rainbow, but it was not raining. We found out later that this strange atmospheric anomaly is called a parhelion or, the word I prefer, sundog.

Sundogs are formed by reflection or refraction of sunlight by ice crystals found within cirrus or cirrostratus clouds. These are the thin wispy clouds you sometimes see in the sky that seem to go for miles. Sundogs normally occur, but not always, when the sun is low in the sky, like at sunrise and sunset. The ice crystals within the clouds act as prisms breaking up the light into the different wavelengths producing the spectrum of colors. When the light hits the prism-shaped ice crystals, the white light is slowed down causing it to separate into the different colors. This process is called dispersion. If you want to learn more, here is a great site that goes into all the physics behind sundogs. The link at the bottom of this sites page explains how they are formed.

I didn't have my camera with me, but I pulled a few images from Wikipedia. I have seen only one sundog before. This was my sister's first.

I was so glad to share this unexpected and beautiful event with my sister on Christmas Day!StumbleUpon


Don said...

Very cool! Scott Evans posted some photos on Flickr of a sundog down in the Bloomington, IN area earlier this year. I like your posts about the sky! Bugs and birds are super-duper but the sky is so vast and amazing.

Kenn Kaufman said...

Hi Janet,
Great explanation of the physics behind this beautiful phenomenon. I've seen sundogs only occasionally, and you're right, it always feels like a gift when it happens.

I really like the range of subjects that you write about -- from the most fascinating insects to notable plants and birds to phenomena that take up the entire sky ... and, of course, the human visitors to your park. You communicate the perspective of a great all-around naturalist.