How our calendar got the way it did

by Thomas Larsen

         In the days of the Roman Republic the calendar was numbered from the founding of the city of Rome, which according to the present calendar would be 753 BC. However, this was a complicated lunisolar calendar of only ten moons, or “months” – which totaled 355 days. Lunisolar calendars combined solar year plus moon phase and required a group of people to decide when days should be added or removed in order to keep the calendar in sync with the astronomical seasons, marked by equinoxes and solstices. Unless otherwise corrected, the months would have a tendency to rotate throughout the year and get completely out of sync with the seasons. Consequently, an extra month was inserted from time to time, so the calendar would bear more relation to the position of the sun. Greece, and all of northern Europe, operated on a solar calendar which is based entirely on earth’s revolutions around the Sun. When the Romans invaded Greece in the 5th century BC they realized the advantages of a solar calendar.
         Finally in 45 BC Julius Caesar, a Roman General, switched from a lunar to a solar calendar. He divided the year into 365 days, with twelve months, which alternately had either 30 or 31 days, except February, which was considered an unlucky month, so it had only 29 days. That was all part of these ancient peoples’ superstitions back then. Telescopes were centuries away from being invented. People had only their eyes to view the sky and didn’t even understand that it’s the earth that goes around the sun which gives us our year. They thought the earth was stationary and the sun, moon, planets, and stars all went around the earth. We were the most important, we were at the center. All that up there was made just for us. Some societies even thought the things in the sky were gods or goddesses and the better they understood their motions the better they could worship their gods or goddesses. They would see the constellations and seasons change throughout the year and with that they figured out the year was 365 1/4 days long. Julius lengthened February to a full 30 days every 4 years and leap year was born. Leap days keep our calendar in alignment with earth’s revolutions around the Sun. The calendar then became known as the Julian Calendar. One of the new months was named July, in honor of Julius. But upon his death he was succeeded by the superstitious and egocentric Augustus Caesar, who named a month after himself, August. He then declared that his month should have just as many days as Julius’ month meaning July and August both now had 31 days, no longer alternating between 30 and 31. Now the unlucky month of February had more days than necessary so he shortened it to 28 days. The Julian Calendar remained in existence for many centuries with little change. In the fourth century though, Emperor Constantine established our seven-day week which was based on Jewish tradition.
         Establishing the length of the year down to 1/4 of a day with the limited technology available was amazing in itself. But the length of the year is not 365 1/4 days. It is 11 minutes 14.9 seconds less than that. By adding a day every 4 years too many days get added to the calendar. After 128 years go by 1 day too many has been added.
         In 325 AD, which is when the Catholic church was officially organized, it decreed that the resurrection of Christ should be celebrated at the beginning of spring, when all life was renewed. And the beginning of spring was determined by the vernal equinox. Easter was established as the first Sunday after the first full moon after the vernal equinox.
         By 1582 the 11 minutes 14.9 seconds error in the Julian Calendar had thrown it 10 days out of sync with the sun, which was very upsetting to the Catholic Church, since the calendar determined all their feast days – and particularly Easter, which was a movable feast, but dependent on the vernal equinox. At that time, the Pope was the most powerful person in the world. Pope Gregory XIII had the authority to establish his “Gregorian” Calendar. He deleted 10 days from October that year. Then Gregory modified the rule about how often leap-year must occur so the calendar wouldn’t drift out of sync again. All century years had been leap years up to this point. But now under Gregory 3 of 4 century years will not be leap years – no February 29th for those years. 1600 was a leap year, but 1700, 1800, and 1900 were not. 2000 was a leap year, but 2100, 2200, and 2300 will not be. 2400 will be and on and on. This method is so accurate that it will be some thousands of years before people far in the future will have to make another correction, and that’ll be up to them how they’ll want to do it. It took many years before many other countries adopted the Gregorian Calendar, some not doing so until the early 20th century. America did so in September 1752. By then the discrepancy between the calendars had grown further, requiring now 11 days to be skipped.
         But wait, there’s more. To figure which particular years would be leap years and which century years would not be brings mathematics into the equation. To be a leap year, the year number must be evenly divisible by 4 – meaning divide 4 into a year number. If the answer is a whole number (with no decimal remainder) that year is a leap year. To be a leap year in a century year, the century year number must be evenly divisible by 400 – meaning divide 400 into a century year number. If the answer is a whole number (with no decimal remainder) that century year is a leap year. So there you have it. All you young people out there who could live to the year 2100 when you have no February 29th just remember you heard the reason why from me first.   

Compiled from information available on various Web sites