It’s happening again: The champagne. The ball dropping. The resolutions of everything we plan to change.
But what are we really celebrating on New Year’s Eve? And why do we consider tonight - of all nights - as the last night of the year?
According to Denis Feeney, author of "Ceasar’s Calendar: Ancient Time and the Beginnings of History," time-keeping is part of what makes us human.
"Every society attempts to track time," he said. "Even the first societies discovered in the middle of Papua New Guinea know when to plant and when to harvest. No one just drifts through time, not even hunter-gatherers."
For much of human history, each locality came up with its own way of marking time and its own date for when a year ended. Many cultures - including the Aztecs and Babylonians - celebrated the new year in March, just before new crops were planted. Indeed, the Persian calendar marks the new year, Nowruz, on March 21, with feasts and bonfires meant to cleanse bad things from the previous year. In Bali, people open their new year with a day of silence, which falls on March 31 this year.
Even early American colonists celebrated New Year’s Day on March 25, until the date was officially changed in 1752. That date had a Christian logic to it: It’s exactly nine months before Christmas.
So how, then, did we come to celebrate the new year in winter, when nothing is blooming and the world doesn’t feel new at all?
According to Feeney, the Romans made the change. Initially, they, too, celebrated New Year’s Day in March. Chief executive officers in Rome used to take office in March, at the beginning of the year. But around 153 BC, they began taking office in January. Why remains a mystery.
"The best guess is that you have got the winter solstice in late December," Feeney said. "That’s the shortest day of the year." It’s a logical start to the countdown toward spring. But nobody knows for sure why the Romans switched the first month to January and named that month after Janus, God of endings, beginnings and doorways.
By the time Julius Caesar got himself elected chief priest at age 37, Jan. 1 was already the first day of the year.
But at the time, the Roman calendar tracked the moon, not the sun. A year had only 354 days. To keep the calendar in tune with the seasons, the chief priest had to insert an extra 20 days into the month of February every couple of years.
"It was not precise," Feeney said. "But it was good enough."
The trouble was that Caesar spent a decade fighting wars in distant lands. He couldn’t add days to the calendar while he was away. Time grew increasingly out of whack. The month of March, which everyone knew to be spring, began appearing mid-winter, as snow fell.
Caesar pondered the problem and discovered a solution. While visiting Cleopatra in Egypt, he met an astronomer who suggested a calendar based on the sun. It had 365 days, and a leap year with an extra day in February every four years.
The year Caesar made the reform was called the "last year of confusion." It was 445 days long. But once he got Rome on track, the new calendar worked well. It eventually spread across Europe through the Catholic Church. But Caesar’s calendar contained a tiny flaw: A solar year is actually made up of 365 days, 5 hours, 48 minutes and 46 seconds. This adds an extra day every 130 years. Over a millennium, the discrepancy starts to matter.
So, in 1582, Pope Gregory - who inherited Caesar’s mantle as chief priest and keeper of time - announced a tweak: a 0.002 percent correction in the length of a year.
Catholic countries immediately adopted the change. But Protestant countries, including Britain, took centuries to get on board. Britain’s House of Commons adopted Gregory’s calendar in 1752. American colonists followed suit.
So, tonight, as you toast your own new beginning, take a moment to consider the miracle of collective human experience across the ages. The fact that billions around the world take tomorrow to be the first day of something new is nothing short of astonishing.
Boston Globe columnist Farrah Stockman can be reached at fstockman