Our calendar has been in effect for thousands of years, right? Wrong! The calendar we use today has been in use for only about 250 years.
Almost all civilizations of ancient times used “natural” divisions of time. There are three of them. The first is the day—the time for the earth to rotate on its own axis. The second is the month—the time for the moon to rotate around the earth (about 29.5 days).
The third is the year—the period of rotation of the earth around the sun (about 365.25 days).
The problems arise because these three do not fit together in any simple way.
The first Roman calendar had 10 months. We still retain the names of the seventh to 10th months as September, October, November, and December. But 10 months made for a very messy time division so in the first century B.C., two more months were added.
Now a real month is 29.5 days. The Romans knew that, of course, so they made half the months with 29 days and half with 30—an average of 29.5. But there was another snag. The total of these months added up to only 364 days.
To make up for this, the Romans put in an extra month every once a while—a sort of “leap month.”
This extra month became a political football in Rome. Sometimes it was used to collect an extra month’s taxes, or to keep conscripts in the army an extra month.
Needless to say, it was not a very popular thing among the ordinary citizens of Rome.
So Julius Caesar, fed up with this state of affairs, ordered a new calendar to be drawn up. This still had 12 months but they had 28, 30, or 31 days each. He also instituted leap year, with an extra day, to take care of that extra quarter day in the sun’s year.
The Romans later renamed two of the months in the summer to commemorate Julius Caesar and Caesar Augustus. Hence we now have July and August.
A small error still remained because the sun’s year actually has an extra 11 minutes (which we didn’t mention before). Now 11 minutes isn’t very much but by 1582, these minutes added up to 10 days. As such, spring was coming on March 11 instead of the 21st, and the same thing was happening to autumn, winter, and summer.
So further reforms were instituted by Pope Gregory in 1582. Some of them were very complicated but there was one simple one to put things right. The day after Oct. 4 was declared to be Oct. 15 in 1582.
All of the Catholic countries in Europe adopted this right away but the Protestant ones did not. England, for example, did not adopt this calendar until 200 years later.
This meant that a traveller could go from France (a Catholic country) to England (a Protestant one) and lose 10 days in doing so. But in 1752, England and all of her empire, including the very large American colonies, did adopt the calendar we now use.
Russia didn’t adopt it until after the revolution (1917) when they had to drop 17 days to get in step with the rest of the world.
So our modern day calendar is indeed based on the one originally devised by the Romans but it has been modified and corrected a great deal in the meantime.
As of now, the error is only one day in 40,000 years.