History and science of Groundhog Day
According to this excellent Groundhog Day site, German settlers arrived in the 1700s to an area northeast of Pittsburgh, Pa. that had been settled previously by the Delaware Native Americans. The Germans celebrated Candlemas Day, originally a Medieval Catholic holiday, to mark the mid-point between the Winter Solstice and the Spring Equinox in the Northern Hemisphere. The holiday also has roots in Celtic-Gaelic and Pagan cultures, where it is celebrated as St. Brigid’s Day and Imbolc, and is a time of festivals, feasting, parades, and weather prediction, as well as candles and even bonfires to mark the sun’s return.
According to Wikipedia, “Imbolc” comes from an Old Irish word meaning “in the belly.” Among agrarian people, Imbolc was associated with the onset of the lambing season.
The German settlers of Pennsylvania put candles in their windows and believed that if the weather was fair on Candlemas Day then the second half of winter would be stormy and cold. While this has always seemed counter-intuitive to me, this site explains the science of Groundhog Day and that cloudy weather is actually milder than clear and cold. It makes sense, then, that the shadow would portend six more weeks of winter. (A lifelong mystery is solved.)
The English and Scottish had wonderful sayings to mark this occasion:
The serpent will come from the hole
On the brown Day of Bride,
Though there should be three feet of snow