Secrets of Dating: Julian vs Gregorian calendars

There is often a difference of 11 to 13 days between the date an event occurred in history and the date it is celebrated on the calendar today. This is due to a discrepancy that occurred in the shift from the Julian to the Gregorian Calendar.

The Julian Calendar, named for Julius Caesar, called for an extra day (Leap Day) to be inserted once every four years, in order to keep consistent with the 365 & 1/4 day solar year.

It was a vast improvement over the previous Roman calendar, which drifted up to 100 days from the actual solar year. However even the Julian calendar wasn’t entirely accurate. The solar year is slightly less than 365 & 1/4 days. Not enough to notice at first. It took almost a century for the Julian Calendar to drift just one day from the solar year.

But by the 1500s people were starting to notice that the calendar was off by 11 days from the summer and winter solstice.

Astronomers calculated that to accurately mirror the solar year, one Leap Day had to be removed each century. In other words, each century should have 24 Leap Years rather than 25. The new calendar was called the Gregorian calendar, because it was installed under Pope Gregory’s Papacy in 1582 AD. [This is why years ending in ’00 no longer have Leap Days. (Except every 400 years which is why 2000 was a Leap Year. {Just don’t worry about it. You have better things to do with your brain power.}

Anyway to get rid of the 11 excess days that had accumulated over the previous 15 centuries Pope Gregory did just that. He tossed 11 days from the 1582 calendar. This means people went to bed on October 4th, 1582 and woke up on October 15th. (And you thought Daily Savings was a drag!)

It took Great Britain and its colonies another 200  years to adopt the Gregorian system and get rid of the 11 days. Russia didn’t adopt the Gregorian calendar until 1918. Which is why the Russian “October Revolution” of 1917 took place on November 7 according to Western calendars.

It’s been suggested that the Austrians were annihilated at Napoleon’s Battle of Austerlitz because of the Julian vs. Gregorian calendar debacle.  Reinforcements from Russia thought they had eleven extra days to make their rendezvouz with the Austrians.

So if you see holidays celebrated 11 to 13 days after the rest of the world, it’s because the Eastern Orthodox Churches celebrates according to their pre-Gregorian dates. (Christmas, Epiphany, New Year…)

And remember, if you ever miss a birthday by several days, just tell ’em you’re on the Julian calendar. It’s old school.

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