Here’s the thing: Earth is a bit of a show-off with its orbit. It takes about 365.2422 days to circle the sun, not a neat 365. That extra quarter-day adds up, and if we ignored it, our calendar would drift. Can you imagine Christmas in July? Exactly.
Julius Caesar first tried to fix this with the Julian calendar, but he made it too simple. By 1582, we were ten days off, so Pope Gregory XIII stepped in with our current Gregorian calendar. Clever, right? It drops three leap days every 400 years to keep things tight.
