Wednesday, February 29, marks leap day, a day that's added to the month of February almost every four years—that is, every leap year—to keep the modern calendar in line with the celestial cycles that frame it.
But where did leap year come from? How does it work? And have other cultures, with their own systems for tracking time, needed to use it, too?*
Have you ever asked any of the above questions? If so, click here to read the full explanation from National Geographic.
*Written by Brian Handwerk, National Geographic Magazine, 2008
