September 11th marks the passing of French astronomer Joseph-Nicolas Delisle. Among his accomplishments, he was the person who proposed the mechanism behind the sun dog phenomenon. Sun dogs, or "perhelia" are the bright rainbows that occasionally occur on either side of the sun. They are formed when ice crystals form in the upper atmosphere and reflect the sunlight. If the sun is high enough, a halo or ring can form around the sun. Moon dogs are the same phenomenon at night with the moon.
I am not sure of the origin of the term "sun dog". I have seen references in Greek and Chinese mythology, but have not found any definitive origin. Pass along any stories you have heard about it and find out what else occurred on this day in science history.
No comments:
Post a Comment