gen-explain-the-julian-versus-gregorian-calendar-as-you-would-to-e7da

Explain the Julian versus Gregorian calendar as you would to a capable student, in 3-4 sentences.

# Julian vs Gregorian Calendar The **Julian calendar**, introduced by Julius Caesar in 45 BCE, established the 365-day year with a leap year every four years, giving an average year length of 365.25 days. However, the true solar year is actually about 11 minutes shorter (365.2422 days), so the Julian calendar gradually drifted out of sync with the seasons—accumulating about 3 extra days every 400 years. To fix this error, Pope Gregory XIII introduced the **Gregorian calendar** in 1582, which keeps the leap year system but skips leap years in century years unless they're divisible by 400 (so 1700, 1800, and 1900 weren't leap years, but 2000 was). This correction keeps our calendar aligned with Earth's orbit around the sun, which is why nearly the entire world uses it today.