It may seem random that Groundhog Day falls on the second day of February, but, if we look at its roots in astronomy, it's actually the perfect day to have spring on the brain. Groundhog Day is tied to the seasons for a very important reason — and it's probably much older than you'd guess. Groundhog Day as we know it started in the 1800s , when a couple of Pennsylvanians went out to the woods to see if the groundhogs had woken up for spring yet. They were actually spending the day observing Candlemas , which celebrates the day that the baby Jesus was presented to God. This is not the only holiday that shares February 2 with Groundhog Day — people have been celebrating this time of year for centuries, even millennia. Groundhog Day is simply the latest occasion. According to EarthSky , Groundhog day occurs on a "cross-quarter day," or a day that falls exactly between a solstice and an equinox. There are four cross-quarter days in the year, plus the four "quarter" days (the spring equinox, summer solstice, fall equinox, and winter solstice). Throughout history, cross-quarter days have been celebrated as signs of the changing seasons. For example, the Pagan holiday Imbolc dates back to Celtic customs, falls on the same cross-quarter day as Groundhog Day, and celebrates the arrival of spring. Cross-quarter days are viewed as reminders to embrace inevitable change and to prepare for the rest of the year. Using a groundhog to predict the seasons isn't all that random, either. As those Candlemas-celebrating Pennsylvanians knew, these adorable rodents come out of hibernation at the very first signs of spring. So, we can trust them to stick to the astronomical schedule. It'd be pretty cool if groundhogs had special weather sensors in their brains, but the whole shadow thing is pure superstition. It was simply believed that sunny days signaled a long, cold winter, while cloudy days suggested that warmer weather was on its way. So, while you're cursing (or celebrating) Punxsutawney Phil's prediction tomorrow, remember that he's actually honoring a very old tradition, ingrained in human faith. Of course, that doesn't mean you can't be mad if he calls for six more weeks of winter.