Spring, summer, fall and winter – the seasons on Earth change every few months, around the same time every year. It’s easy to take this cycle for granted here on Earth, but not every planet has a regular change in seasons. So why does Earth have regular seasons when other planets don’t? Gongjie Li, assistant professor in the School of Physics, explains about axial tilts of planets, which have big implications for everything from seasons to glacier cycles, since that tilt can determine just how much sun a planet will get. The magnitude of that tilt can even determine whether a planet is habitable to life. (This article by Li was also reprinted in in IFL Science, Qrius, and the Longmont (Colorado) Leader.)