This Friday will be the 132nd official Groundhog Day in the United States. Celebrated in Canada, Germany, and the U.S., the holiday derives from a long-standing German-Dutch tradition, which we’ve been officially recording since 1886. The basic idea: if a groundhog emerges from his hole and sees his shadow, winter will last for six more weeks, but if he sees no shadow, an early spring is on the way.

Why are we discussing this arguably adorable tradition on a *science blog*, you ask? Although there’s much we can learn about the tradition (and lots of lore!), Groundhog Day is our post topic this week because it’s a great way to explore the basic concepts of *probability*. Scientists use probability theory every day in their research, most notably, to make sure that the phenomena we are studying are not due to random chance. Probabilities can be complex, but even in their simplest form — as is the case with Groundhog Day — the questions we can answer using probability theory are often quite interesting. (more…)