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Most of us aren’t aware of the fascinating history of something we use every day—the Gregorian calendar. Pope Gregory XIII introduced it in 1582 to modify the inaccurate Julian calendar that was devised in 46 BC. Julius Caesar had introduced the Julian calendar to replace Rome’s ten-month calendar from 750 BC. That one was attributed to Romulus, the founder of Rome.
The calendar of Romulus
The ancient Roman calendar had ten months of 30 or 31 days:
March, named after Mars, the Roman god of war
April, thought to be named after Aphrodite, the Greek goddess of love
May, named after the god Maia, the mother of the Greek god Hermes
June, named after Juno, the queen of the Roman gods
July, originally named Quintilis, meaning fifth month
August, originally named Sextilis, meaning sixth month
September, seventh month
October, eighth month
November, ninth month
December, tenth month
An additional winter season of two months was apparently adjusted as needed to keep the calendar accurate.
The calendar of Julius Caesar
The Julian calendar is said to have been updated based on the more accurate Egyptian calendar. It added two months to the winter cycle, January—named after Janus, the god of openings or beginnings, and February—named after the Roman god Februus, based on the festival of purification.
The Romans renamed the months of Quintilis and Sextilis as July to commemorate Julius Caesar, and August to honor Augustus Caesar. Other emperors tried to take possession of other months, but none of their claims would endure.
In addition, the Julian calendar added a leap day every fourth year because the trip around the Sun didn’t take exactly 365 days. This gave the calendar year a length of 365.25 days.
The adjustment of weekdays
The old Roman calendars originally contained eight-day weeks. These eventually shifted to seven-day weeks as Romans encountered more agreeable time keeping systems in other cultures. In Christianity, by the second century AD, Justin Martyr wrote that Christians in his region were meeting on the Day of the Sun.
In AD 321, Roman Emperor Constantine officially decreed a seven-day week that the Babylonians had originally introduced around 600 BC. The week began on Sunday and ended on Saturday. Each day was named after a different observable heavenly body—Sun, Moon, Mars, Mercury, Venus, Jupiter, and Saturn.
In Germanic countries, the name of Anglo-Saxon and Nordic gods replaced some of the planetary names and we ended up with Tiwesday, Wodensday, Thorsday, and Frigeday, which in English became Tuesday, Wednesday, Thursday, and Friday.
The reasons for the Gregorian calendar
The Gregorian calendar was needed to correct a minor error in the length of the solar calendar which complicated the dating of Easter Day. In the fourth century Christians had decided to date Easter on the first Sunday after the full Moon following the spring equinox. There was not to be a specific date each year for Easter. This was to keep the day synchronized with the Jewish Passover, which is determined the same way. This process not only shows the importance of astrology in the lives of ancient people, but the way Christians overlaid their holidays on the sacred days of other cultures. By the time of the Gregorian modification, Easter fell eleven days earlier than it should have.
The new calendar kept the leap day concept but didn’t allow so many of them. It skips three leap days every four centuries. This change made the calendar year much closer to the actual solar year. The solar year is about 365.2425 days, and the new calendar is only off by .0003 days or 26 seconds per year. That is one day every 3,030 years, whereas the Julian calendar had been off one day every 128 years.
Adopting the Gregorian calendar
Since the current calendar was established by a Catholic pope after the Protestant Reformation, the Catholic countries in Europe and their colonies were the first to adopt it. It would take over three centuries for the rest of Europe to fall in line, with Greece being the last European country to fully adopt the “new” calendar in 1923.
Because of this discrepancy, Easter was celebrated in different countries and principalities on different days. In fact, even now, some Eastern Orthodox countries base their Easter celebrations on the Julian calendar.
The Gregorian calendar has become the worldwide calendar and the last country to adopt it was Saudi Arabia in 2016.
One of the impediments to adopting the new calendar was that in order to make up for past errors, ten days had to be eliminated. When the calendar first became official, the date skipped ahead from October 4 to October 15, 1582, in one night. But the day of the week, Friday, remained the same. This advancement of the calendar happened in the British colonies—the current United States and Canada in 1752. It also happened in Alaska in 1867 when the United States acquired the territory from Russia.
People had to deal with all kinds of problems, such as lost birthdays, anniversaries, business meetings, etc. due to this “spring ahead.” It must have caused more confusion than we experienced in the year 2,000 (Y2K) changeover.
The beginning of the year
As if things weren’t confusing enough, January 1 wasn’t always the beginning of the new year. After the decline and fall of the western Roman Empire in the fifth century, many Christian regions adjusted their calendars to begin the new year on March 25 or December 25 since they were Christian holy days. One of the other things that the Gregorian calendar accomplished was restoring January 1 as the first day of the year.
So, you will probably never look at that familiar calendar on your wall the same way again. Now you can educate everyone you know about the odd history of that amazing chart and appreciate all the complex scientific work that determined it.