You can look up any date and invariably find something interesting that occurred on that day in history.

For example, if you were to look up today’s date, Oct. 5, you would find that it was the date of Tecumseh’s death in 1813, in 1857 the city of Anaheim, Calif., was founded, Harry Truman gave the first televised White House address in 1947 and Larry Fine (of The Three Stooges) was born on this date in 1902.

But if you were to look up this date in history in the countries of Spain, Portugal, Italy or Poland, you would come up empty handed — for one year at least.

As odd as it sounds, in those four countries — in the year 1582 — Oct. 5 does not exist.

How, you may ask, is that even possible?

The answer is deceptively simple and yet fascinating all the same: Oct. 5, 1582 is the date the Gregorian calendar was first introduced — and there’s no “day zero.”

The Gregorian calendar was introduced as a replacement for the slightly flawed Julian Calendar and is named for Pope Gregory XIII. And while the Gregorian retained the same months (and month lengths) as its predecessor, in the “newer version” years that are evenly divisible by 100 are not leap years — except that years evenly divisible by 400 remain leap years.

Confused? Don’t worry about it. Basically, what it all means is that had we stuck with the Julian calendar, today, we would be 13 days behind where we are on the Gregorian.

If you think it’s strange that Oct. 5 “didn’t exist” in parts of Europe in the year 1582, it’s about to get even stranger — neither did the next 10 days.

According to history, a Jesuit mathematician and astronomer named Christopher Clavius was asked to head a commission that originally proposed the Julian calendar be, let’s just say, updated.

As was mentioned earlier, the solution decided upon by the commission was to add a “leap day” three different times every 400 years. The result of all this crazy math was a 365.2425-day year — which was really close to what astronomers had determined to be the average solar year of 365.2424 days.

But, to restore March 20 or March 21 as the day of the lunar equinox — moon phases were a big thing back then — old Clavius went to the Pope and suggested that 10 days be … well, skipped.

The Pope agreed and issued the edict that Oct. 5 through Oct. 14 be omitted from the calendar in 1582.

Today, the Gregorian calender is used by most of the world and is generally agreed upon as the “civil” calendar. Still, there’s plenty of exceptions including the Chinese, Hebrew, Hindu and (yep, it’s still there) Julian calendars which are primarily used for religious purposes.

The Persian (Iranian) calendar is still used in Iran and a few parts of Afghanistan and the Ethiopic calendar remains the principal calendar used in Ethiopia and Eritrea. In Somalia, the Islamic and Somali calendars are used in conjunction with the Gregorian and in Thailand, although the months and days have adopted the Gregorian style, the years are still based on the traditional Buddhist calendar.