gen-define-the-julian-versus-gregorian-calendar-and-give-one-sho-5919

Define the Julian versus Gregorian calendar and give one short worked example.

# Julian vs Gregorian Calendar ## Definitions **Julian Calendar:** Introduced by Julius Caesar in 45 BCE, it has a simple leap year rule: every year divisible by 4 is a leap year. This gives an average year length of 365.25 days. **Gregorian Calendar:** Introduced by Pope Gregory XIII in 1582, it refined the leap year rule: years divisible by 4 are leap years, EXCEPT century years (divisible by 100) must also be divisible by 400. This gives an average year length of 365.2425 days, closer to the true solar year. ## Worked Example **Question:** Was the year 1900 a leap year? **Julian Calendar:** - 1900 ÷ 4 = 475 (evenly divisible) - **Yes, leap year** ✓ **Gregorian Calendar:** - 1900 ÷ 4 = 475 ✓ (evenly divisible) - 1900 ÷ 100 = 19 ✓ (century year, so check next rule) - 1900 ÷ 400 = 4.75 ✗ (NOT evenly divisible) - **No, NOT a leap year** ✗ This is why the two calendars gradually drift apart—by about 3 days every 400 years. By 1900, the Julian calendar was already 13 days behind the Gregorian.