Groundhog Day is a popular, albeit unofficial, holiday in North America. It revolves around the superstition that a large rodent of the family Sciuridae is capable of predicting the weather.
 The ritual
The basic idea is that on February 2nd, people gather around to watch a groundhog with a stupid, alliterative name come out of its hole. According to legend, if the groundhog doesn't see its shadow (if it's cloudy, or the groundhog is nearsighted), an early spring will come. If it's a sunny day or the lights from the TV cameras are too bright, it sees its shadow, retreats into its home and six more weeks of winter will follow. Some people believe that this is actually an accurate form of weather forecasting.
The "six more weeks of winter" legend is particularly good for identifying people who are bad at math and/or dates. Exactly six weeks (42 days) after February 2nd is March 16th (March 15th in leap years)...only a few days before the vernal equinox (e.g., the end of winter).
Of course, if you're in the southern hemisphere, this is all completely meaningless.
 The film
Groundhog Day is also a comedy film starring Bill Murray, where the central character is forced to relive the same day over and over, specifically, Groundhog Day. The term "Groundhog Day" has since been used to describe the effect of reliving the same moment repeatedly which is often used in science fiction as a plot device. It is a rather good film, and well worth watching.
A version of this plot, with a few major differences, was first written in 1905 (published in 1915) as The Strange Life of Ivan Osokin by P.D. Ouspensky. In this book a man who repeatedly relives his life is, unlike the Bill Murray character, unable to make significant changes.
"Spring" is a Canadian term, which means "eight more weeks of winter".
 External Links
- Straight Dope article on Groundhog Day (Spoiler alert: It's not a very good tool for predicting the weather)