For most people alive today, the calendar is just the calendar. While not every country uses the same one, most of the world is at least aware of what is called the Gregorian Calendar, and they follow it without giving it much thought. In fact, most people may not even know that it had a name other than just ‘the’ calendar.

Throughout history, however, there have been quite a few different calendars created in order to try to keep track of the years. Some were based on Lunar cycles, others (including the Gregorian) are based on solar cycles, and still others are based on different things altogether.

The Gregorian Calendar has only been in use since 1582, which is pretty recent in terms of all of human history. So, why was the calendar changed at the time? It is an interesting story.

Prior to the change, the Catholic Church (and most of the rest of the world) was using the Julian Calendar, which was implemented by Julius Caesar in 45 BCE.

For its time, it was a remarkably accurate calendar, which allowed the world to keep things on track. Unlike previous calendars, it used the concept of leap years to offset the fact that a year is not exactly 365 days. So, Caesar said that every four years, a day would be added to keep the seasons as they should be.

This worked for over 1500 years, but when it comes to calendars, very accurate isn’t accurate enough.

In the 1500s, the Catholic Church noticed a problem (well, it was noticed long before, but it now needed to be solved).

Since the Council of Nicaea, which took place in 325 CE, the Church has held that Easter would always fall on the first Sunday after the first full moon after the spring equinox on March 21st.

No problem, until the slow drift of the Julian Calendar made it so the spring equinox did not fall on March 21st. So, rather than allowing calendars to continue to slowly drift like this, Pope Gregory XIII worked with astronomers and scientists to come up with a calendar that was far more accurate than the Julian one.

In the Gregorian Calendar, there is a leap year every four years, unless the year is divisible by 100. To make it even more accurate, they added in a rule that if the year was not divisible by 400, it would still be a leap year.

It may sound convoluted, but in reality, these rules have almost perfectly solved the problem of calendar drift.

The Pope decided to implement the use of this calendar throughout the Christian world, starting in October, since there were no important feast days at that time.

Everyone went to bed on October 4th and woke up on October 15th. Eliminating those 10 days put Easter back where it belonged, and the calendar won’t fall out of sync for thousands of years thanks to this new system.

To make this story even weirder, not all of the world made the switch. Some places, including Russia, stayed on the Julian Calendar. So, when the United States bought Alaska from the Russians, their calendar had to be updated.

This is why on Alaskan calendars, the missing 10 days occur in 1867.

For those who are interested, you can ‘see’ the missing 10 days by scrolling your calendar app all the way back to October of 1582.

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