How Was The Calendar Invented?

Have you ever wondered why we use the calendar that we use? Why are there 365 days in a year?

If people on Earth speak thousands of different languages, how is it that most of us use the same calendar? The reason the Gregorian calendar is the international standard used almost everywhere in the world to mark the passing of time might be a little more complicated than you might have thought. It takes 365 days, 5 hours, 48 minutes and 46 seconds for the Earth to make a full revolution around the sun; Things would be a lot easier if it was an even 365 days.

Most of the Western word used the Julian calendar, which was put into place and named after Julius Caesar on 45 BCE, which was the year 709 for them since their calendar started on the year Rome was founded). The Julian calendar had 365 days every year with an extra day every four years. This was pretty accurate, but made a year on average 11 minutes and 14 seconds too long. This little glitch wouldn't be dealt with until 1582.

That's the year that the Gregorian calendar (also known as the Western or Christian calendar) started finally being used. That 11-minute glitch in the Julian calendar created a problem with Easter. It was supposed to be celebrated on the Sunday after the first full moon after the spring equinox, or March 21st. But as it slipped later and later each year, Pope Gregory got concerned, so he commissioned Italian scientist Aloysius Lilius to "fix it". After crunching the numbers, he realized that the Catholic world had to skip ahead ten full days to catch up.

The Gregorian calendar is more accurate than the Julian because it still had a leap year every four years, except for years that are divisible by 100, and unless that year is divisible by 400 (so 2000 was a leap year, but 2100 will not be.) Of course, nothing's perfect, and the Gregorian calendar is no exception: in 4909, is will be a full day ahead.

The reason it's 2015 and not 2768 is because in the year 525, Christian Monk Dionysius Exiguus determined that Jesus was born in the Roman year 753, and reset the year from there (although it's generally accepted that he was off by about 5-6 years). We can also blame Exiguus for the denominations BC (before Christ) and AD (Anno Domini, Latin for "The Year of Our Lord"). Academic and scientific communities have been increasingly using the more neutral, less Christianity-centric BCE and CE for "Before Common Era" and "Common Era".

Of course, there are tons of other calendars that people use, and even some more-exacting calendars that some propose adopting (like the Tranquility calendar, which starts on the day we landed on the Moon, and has 13 28-day months, all named after scientists). Do you use rely on any other calendars, like a lunar or religious one? Please let us know in the comments below--we'd love to hear from you.

Follow Julian on Twitter: @jhug00

Read More:
6 Things You May Not Know About the Gregorian Calendar (
"If you were living in England or one of the American colonies 260 years ago, this date-September 13, 1752-didn't exist. Neither did the 10 days preceding it."

From the Julian to the Gregorian Calendar (via Time And Date)
"The Gregorian Calendar, also known as the ‘Western Calendar' or ‘Christian Calendar', is the most widely used calendar around the world today."

The Curious History of the Gregorian Calendar (via Info Please)
"September 2, 1752, was a great day in the history of sleep."

History of the Roman (Julian) Calendar (via Info Please)
"The Romans were superstitious that even numbers were unlucky, so their months were 29 or 31 days long."