From October 5 to October 14, 1582, nothing happened in Italy, Spain, Portugal, and other parts of Europe. Nobody was born, nobody died, and nobody fell in love because those ten days simply did not exist. When people went to bed on October 4, they awoke on October 15 as their nations adopted the Gregorian calendar we still use today.
Calendar Drift
Most people think a year is 365 days long, with an extra day added every four leap years. But the Earth does not travel around the sun in exactly 365.25 days. The trip actually takes about 11 minutes and 14 seconds less than that, or 365.2422 days.
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The 365¼-day Julian calendar was introduced by Julius Caesar after astronomers in Alexandria realized the older Roman calendar had drifted badly out of sync with the seasons. Even though the Julian calendar was much more accurate, those extra eleven minutes slowly added up over time. The slight difference between the solar year and the Julian Calendar caused it to drift by a day every 128 years. By 1582, the calendar had drifted ten days out of sync with the seasons.
The Gregorian Calendar Reform
Astronomers convinced Pope Gregory XIII, the leader of the Roman Catholic Church, that the calendar needed to be corrected. Catholic nations quickly adopted the new Gregorian calendar, but England and its American colonies refused to accept a calendar introduced by a Catholic pope. They continued using the older Julian calendar until 1752.
Leap Years and Calendar Adjustments
February usually has only 28 days, but the month lasts a day longer in what we call “leap years.” Years divisible by four are usually leap years. Centennial years, which are years that end in 00, are not leap years unless they are divisible by 400. This means that 2000 was a leap year, but 2100, 2200, and 2300 will not be.
The Gregorian calendar is so accurate that it drifts by only about one day every 3,300 years. Someday, perhaps around the year 4883, people may once again have to adjust the calendar, but it is unlikely to be seen by anybody alive today.
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Mr. Donn has an excellent website that includes a section on Geography.
Cite this page:
Dowling, Mike, “Fixing the Calendar,” mrdowling.com, September 17, 2026. Web. [Date of access].
Sources:
Pope Gregory XIII, papal bull Inter gravissimas (1582)
Duncan Steel, Marking Time: The Epic Quest to Invent the Perfect Calendar (John Wiley & Sons, 2000)