Did you know that the dates October 5 to October 14, 1582 don’t exist? They never happened.

I’ll explain in a minute. 

Since we are starting a new year, I got curious about our Gregorian Calendar, what we use around the world to label the dates of each day, what makes today New Year’s Day. 

There are other calendars. Chinese New Year occurs on a completely different date than the Gregorian one. There’s the Jewish or Hebrew Calendar. The old Julian Calendar too. How do these various calendars work? Why do we agree that today, January 1, is the beginning of a new year? 

Here’s what I discovered.

Some 86 calendars have existed over time, some still in use. They fall into four categories:  lunisolar, solar (or tropical), lunar, and seasonal. They’re defined as their Latin roots imply. Lunisolar dates consider both the Moon phase and the position of the Sun in the Earth's sky (or the time of the solar year). A seasonal calendar is a visual method of showing the distribution of seasonally varying phenomena (for example, economic activities, production activities, problems such as debt, illness/disease, migration, and natural events/phenomena, plant growth, etc.) over time. 

In the time of Homer in ancient Greece, each city-state had its own calendar that was based on the cycle of the moon (Lunar), but also the various religious festivals that occurred throughout the year (seasonal). It was divided into twelve months and was 354 days long. The months had completely different names than ours.

The Athenian months were named Hekatombion, Metageitnion, Boedromion, Pyanepsion, Maimakterion, Poseidon, Gamelion, Anthesterion, Elaphebolion, Munychion, Thargelion, and Skirophorion. That’s a mouthful!

Romulus, the legendary first ruler of Rome, is supposed to have introduced the next calendar that predates our own in the 700s BC: The Republic calendar. It consisted of ten months and 355 days, a shortfall over four years of (10+1⁄4 × 4) = 41 days.

The ten months were named Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, and December. Most of these sound familiar! The last six names were taken from the words for five, six, seven, eight, nine, and ten. 

That calendar was replaced by the Julian Calendar in 46 BC, named for Julius Caesar. Designed with the aid of Greek mathematicians and astronomers it was much more accurate with moon and sun cycles. January and February were added and the year was 365.25 days. 

And January 1 became New Year’s Day.

The Julian calendar lasted for over 1,500 years. But there was a problem.

It assumed incorrectly that the average solar year (the time that the Sun takes to complete a full cycle of seasons) is exactly 365.25 days long, an overestimate of a little under one day per century. 

Thus, in October 1582, the Gregorian Calendar came into existence. It contains an average of 365.2425 days per year. When Pope Gregory XIII introduced it, he skipped from October 4 to October 15 so all phases of the moon and sun fell in the right place. It remains the calendar that most of the world uses now.

January 1 remained the first day of the new year.

However, New Year’s Day is not celebrated today everywhere. Chinese New Year, the Islamic New Year, Tamil New Year (Puthandu), and the Jewish New Year are all on different dates, according to their own calendars. India, Nepal, and other countries also celebrate New Year on dates according to their own calendars that are movable in the Gregorian calendar.

The Chinese New Year is lunar and falls any time between our Gregorian January 21 and February 21. 

The Islamic lunar year is eleven or twelve days shorter than the Gregorian solar year, so the date changes every year. In 2022, Islamic New Year will be celebrated on July 30.

The Tamil New Year is celebrated in the South Indian state of Tamil Nadu, on the first of Chithrai (சித்திரை) (April 13, 14, or 15).

We know the Jewish New Year as Rosh HaShanah. It will take place in 2022 on September 25 to the 27th. The average Hebrew calendar year is longer by about 6 minutes and 40 seconds than the current mean solar year, so that every 216 years the Hebrew calendar will fall a day behind the current mean solar year. The current Hebrew year is 5782. A day in the rabbinic Hebrew calendar runs from sunset to the next sunset.

The Iranian (or Persian) New Year, called Nowruz, happens on the spring equinox, usually March 20 or 21.

The New Year of the Zulu people occurs on the full moon of July.

And there’s a bunch of others.

I think this is cool. Our calendar is an invention of humankind, based—as best we can—on the natural cycles of our earth. But we take it for granted that this is just the way it is when we name each day. 

We assume without questioning that today is the start of a new year, when really, the new year could start on any day if we say it does. It could go from spring to spring or fall to fall. The Babylonians celebrated New Year’s Day in late March on the first new moon following the vernal equinox, the day with an equal amount of sunlight and darkness. 

So, why January 1? 

According to History.com, Caesar instituted January 1 as the first day of the year, partly to honor the month’s namesake: Janus, the Roman god of beginnings, whose two faces allowed him to look back into the past and forward into the future. Romans offered sacrifices to Janus, exchanged gifts with one another, decorated their homes with laurel branches and attended raucous parties. 

For a while in medieval Europe, New Year’s Day changed. Christian leaders replaced January 1 with days carrying more religious significance, such as December 25 (the anniversary of Jesus’ birth) and March 25 (the Feast of the Annunciation).

Pope Gregory XIII reestablished January 1 as New Year’s Day in 1582.

Right now, the math of the Gregorian Calendar works for us. It corresponds with our rotation around the sun and Earth’s spin. Who’s to say if this will still be the case a thousand or two thousand years from now? Maybe we’ll have a different calendar. Maybe we’ll declare it a new year in an entirely different time of year. 

But for now, today’s the day! 

So, happy New Year and, despite the current Omicron spread (stay safe!), a happy 2022!