The Groundhog Day book of facts and fun

Every February 2nd, people in the United States wait to see if Punxsutawney Phil, a groundhog living in Punxsutawney, Pennsylvania, will see his shadow and predict six more weeks of cold weather. But how can a groundhog predict the weather? And if it's winter, shouldn't he be hibernating? Are such predictions really accurate? Why is February 2nd so special? And do other groundhogs predict the weather?