Why is Candlemas now called Groundhog's Day?
It's no accident that Groundhog Day and Candlemas are celebrated together, for both signify the triumph of light over darkness, spring over winter.
Candlemas was originally a Celtic festival marking the "cross-quarter day," or midpoint of the season. The Sun is halfway on its advance from the winter solstice to the spring equinox. Candlelit processions accompanied the feast day.
Since the traditional Candlemas celebration anticipated the planting of crops, a central focus of the festivities was the forecasting of either an early spring or a lingering winter. Sunshine on Candlemas was said to indicate the return of winter. Similarly, "When the wind’s in the east on Candlemas Day / There it will stick till the second of May."
A bear brought the forecast to the people of France and England, while those in Germany looked to a badger for a sign. In the 1800s, German immigrants to Pennsylvania brought their Candlemas legends with them. Finding no badgers but lots of groundhogs, or woodchucks, there, they adapted the New World species to fit the lore.