What is a Blue Moon?

This is a question I answered over at Teakay's Blog a while ago. There will be a Blue Moon tonight, New Year's Eve 2009, so I thought I'd post a link to it...

• Where did that saying come from - "once in a blue moon?"

Thanks for reading; it'd be great if I could get some new questions coming in to start the new year! One or two in the pipeline, but it's always good to have some in reserve!