If a groundhog sees its shadow on Feb. 2, it means that winter will last another six weeks. Did you ever wonder how this superstition came about?

One source of the legend begins in the British Isles, with legends surrounding the ancient Celtic Cailleach, which means older, wise woman. (Some sources describe her as a pagan goddess, others as a blue hag.)

Cailleach was the keeper of winter, and it was she who decided how long it would last.

Feb. 1, the halfway point between the winter solstice and the spring equinox was the pagan holiday of Imbolc. It was also the day that Cailleach was supposed to decide how much longer winter would last.

If she woke up on Imbolc, she would make sure the weather was bright and sunny so she could gather enough wood to last the rest of winter. But if she slept in and did not wake up that day, her firewood would run out, and she would have to make winter end earlier.

A similar tradition existed in ancient Europe, only instead of a goddess/hag, the forecaster was an animal that slept through the winter, a "sacred badger." A sunny day now meant that the creature would see its shadow, and be so scared that it would run into its hole and not come out for another six weeks, so winter still had another six weeks to go.

The superstition first appears in the United States around the 18th and 19th centuries, among German immigrants who settled in Pennsylvania. As there were no badgers to be found, the groundhog was chosen for the job.

How good is the groundhog at predicting the length of winter? It depends on who you ask.

Those in charge of Groundhog Day festivities claim that it the creature is correct more than half of the time.

A study of predictions made over the years says that the groundhog has been correct roughly a third to a little more than a third of the time, the same percentage one could expect by chance.