That’s because of a quirk of the international date line, the official starting and ending point of each day. The idea of the date line was introduced at a conference in 1884 in which the world sought to create order with the rise of railroads and international travel. The international date line roughly follows the 180th meridian north to south through the middle of the Pacific Ocean. It is located halfway around the world from the prime meridian, which crosses Greenwich, England, in the United Kingdom.

Countries are free to decide which side of the international date line they want to be on—resulting in a line that zigs and zags its way between the North and South Poles.

(New Year isn’t just on January 1. Learn about Lunar New Year.)

Making things even more confusing, countries set their own times. There are currently 38 local times in use, some set off from Coordinated Universal Time (UTC) by 30 or 45 minute increments rather than an hour, says Paul Eggert, a computer scientist at the University of California Los Angeles who maintains the authoritative global Time Zone Database.

Ultimately, if you’re counting in UTC, Eggert says it would take 25 hours for all the inhabited places on Earth to get through a day. Here are the first and last countries to celebrate the new year, and other peculiarities of our global time zones.

First country to celebrate

The first land masses to greet the new year are Kiritimati Island and a string of 10 other mostly uninhabited atolls in the central Pacific Ocean. One of the 33 islands that make up the Republic of Kiribati, Kiritimati is located almost directly south of Hawaii, within the same line of longitude—but celebrates New Year a full day earlier.

(The amazing rebirth of the reefs of Kiribati’s Line Islands.)

That’s a relatively recent development. The international date line once cut through Kiribati, meaning the day could be different depending on whether you were on one of the country’s westernmost or easternmost islands. But in 1995, Kiribati moved the date line so that all of its islands would observe the same day at the same time—and win an influx of tourists wishing to be the first to ring in the new millennium.

Last country to celebrate

The last inhabited places to celebrate are the islands of Niue and American Samoa to the southwest of Kiribati in the South Pacific. The day technically ends an hour later in the U.S. territories of Baker Island and Howland Island, but both are uninhabited, Eggert says. (And if no one is there to see the time change, does it really change at all?)

(Learn about Rosh Hashanah, the Jewish New Year.)

Also nearby, Samoa (not to be confused with American Samoa) was once one of the last countries to ring in the New Year—until 2011, when the country decided to change time zones to align with its trading partners Australia and New Zealand. With the change, Samoa jumped across the international date line to become one of the first countries to celebrate.

More time zone madness

But there are also plenty of time zone oddities away from the international date line. China, for example, has only one time zone even though geographically the country could have as many as five. The entire country formally observes Beijing time—which has proven an inconvenience for cities like Urumqi, which lies 2,000 miles west of the capital. There, the sun may not rise until 10 a.m. Beijing time.

Eggert says this is why, in practice, the city observes two times simultaneously. “Formally it’s on Beijing time like the rest of China but informally most people run in a separate time,” he says.

(Learn about Hijri, the Islamic New Year.)

This also means that if you cross China’s western border on New Year’s Eve, you might have to set your watch back as much as three-and-a-half hours. Why a half hour? That’s because some countries around the world—including Afghanistan, India, and Burma—use half-hour or quarter-hour deviations from standard time.

How does Antarctica ring in the new year?

But ultimately, Eggert says, “the clock doesn’t really matter at the South Pole. When you’ve got a six-month day and six-month night, time is really arbitrary.”