Nothing gets people pumped like ringing in the New Year. For at least four millennia, cultures around the world have made a point to celebrate the next spin around the Sun with colorful festivities and a spirit of optimism for the future.
But while the instinct to party like it's 1999 dates all the way back to 1,999 BCE, the consensus that January 1 should kick off the year is far from universal. Chinese New Year falls between January 21 and February 20 to coordinate with the turn of the Chinese calendar. Many cultures have opted to welcome the New Year in March, around the vernal equinox, to celebrate the blossoming of new life, agricultural fertility, and longer, warmer days. Autumn is also a popular season for New Year's celebrations, such as the Jewish holiday Rosh Hashanah or the Ethiopian harvest festival Enkutatash. Some people welcome the New Year in June, or in April, or according to an ever-shifting lunar calendar.
So given all these conflicting traditions, how did January 1 come to be such a popular candidate New Year's Day? The answer: Julius Caesar. When it came to giving empires total body makeovers, Caesar had it figured out, which is why in 46 BCE, he overhauled time itself.
This was long overdue, because the Roman calendar was a hot mess in those days. It was based on the phases of the Moon, but unlike other societies with lunar calendars, Roman timekeepers failed to keep in sync and up to date, resulting in major inaccuracies and no standardization.
On top of that, the pontifices in charge of regulating the calendar were corrupt, and would sometimes add days in order to interfere with political elections and successions, like some kind of time-based Ponzi scheme. Nobody in ancient Rome would give you the time of day, because nobody could even agree on what day it was in the first place.
Caesar was not impressed, so he consulted with the well-regarded Greek astronomer Sosigenes of Alexandria, who told him to scrap the lunar calendar altogether and go solar. In order to make the switch, Caesar had to hamfist a whopping 67 extra days into the year 46 BCE in order to resolve the discrepancies between the two systems. He just told everybody that there would be a few extra months that year, and to plan accordingly.
But this transitional 445-day-long year was worth it when January 1, 45 BCE—the first day of the Julian calendar—rolled in. The Roman New Year was traditionally celebrated in March, but Caesar agreed with the growing movement that felt January 1 was a more fitting date, for two reasons.
First, it was the day that Rome's two elected consuls, which were like co-presidents limited to a one year term, took office, so it represented the dawn of a new political administration.
But perhaps more importantly, January was named after the Roman god Janus, who was in charge of gateways, transitions, and renewals. He is often depicted as a two-headed god, with one face looking forward to the future, and the second gazing into the past.
The metaphor was not lost on Caesar, and so January become enshrined as a perfect symbolic fit for New Year's festivities. Naturally, Caesar also named the summer month of July after himself, while his heir Augustus snagged August.
As the Roman empire expanded in the following centuries, the Julian calendar became widely adopted across Europe, and is the direct ancestor of our modern Gregorian calendar. While there were a few insurrections to restore the New Year to March during the Middle Ages, January 1 was favored by the designers of the Gregorian calendar, and that's why we still consider it our annual reboot today.
As arbitrary as all that may seem, it turns out that the date also has some accidental astronomical validity because Earth reaches perihelion, or the closest approach to the Sun, around New Year's Day.
This year, for instance, we will be nearest to the Sun at around 5:49 PM Eastern time on Saturday, January 2, at a distance of 91 million miles. After that, the planet will begin our swing back out to its aphelion, or the farthest point from the Sun, reaching it at 11:24 AM Eastern on July 4, when we will be 95 million miles away.
So when you raise your glass at midnight, be sure to toast Julius Caesar, who had a hunch that January 1 was a great time to start the year, and has since been celestially validated for it. And of course, if you wake up tomorrow with a raging hangover, go ahead and blame that on him too.