If you’ve done much traveling, you’ve probably crossed time zones and had to adjust to gaining or losing hours. But have you ever traveled across the International Date Line (IDL)?

Time

Before fast ships, airplanes, phones, and the internet made long-distance travel and global communications both easy and ordinary, people kept time by the sun. That worked fine when staying in or around one general area and not interacting with people further away. However, in the late 1800s, when global commerce and communication technology began to expand, world leaders realized they needed to establish a standard world time and longitude to better deal with each other.

In 1884, a group of nations met in Washington, D.C. at what was called The International Meridian Conference. During this conference, they set time for all regions of the world, beginning with the Prime Meridian, situated at zero degrees longitude. This meridian was adopted as the world’s single “initial meridian” because over two-thirds of ships were already using it for zero longitude.

Did You Know…

• The United Kingdom established the Prime Meridian in 1851, when they were one of the most powerful and technologically advanced nations in the world.
• The Prime Meridian runs through the British Royal Observatory in Greenwich, and so it became known as Greenwich Meridian Time.

Date

The nations at the 1884 International Meridian Conference not only set a standard world time, but also established The International Date Line (IDL). This is an imaginary line running from the North to the South Pole through the middle of the Pacific Ocean. It’s based on the 180th meridian—which divides the earth into Western and Eastern Hemispheres. Far from being a straight line, the IDL zigs and zags, depending on nearby countries’ needs and concerns.

A line of convenience rather than a legal entity, it is the internationally accepted place where one day ends (east side) and another begins (west side). In other words, it marks the place that separates two consecutive calendar dates.

Did You Know…

• The 1884 conference chose to set the IDL at the 180-degree meridian not only because it was halfway around the world from the prime meridian, but because it passed through sparsely populated areas in the Pacific Ocean
• Countries near the IDL can move the line without seeking approval from anyone. They simply publicize the change, so the international community and mapmakers know.
• The 1884 conference’s resolutions are not binding or a matter of international law.
• The island nation of Kiribati straddles the equator. In 1995, the country moved a large part of the IDL east, so all the country’s small islands were together on the same side. They then renamed their easternmost island, Millennium Island, because it saw the new Millennium first.
• Samoa’s move to the western side of the IDL means Samoa and trading partners are all on the same day of the week and are some of the first—rather than last—countries in the world to ring in each new year.
• The IDL was first added to maps by the British Admiralty in 1921.

Time Travel

Crossing the IDL when traveling means doing a little time travel. If you cross the IDL traveling west, you add a day, i.e., Monday becomes Tuesday. But if you cross the IDL while traveling east, you lose or repeat a day, i.e. Monday stays Monday or even becomes Sunday, depending on how far east you travel.

For example: If you were to leave Auckland, New Zealand (N.Z.), today, Saturday, 5/4, and cross the IDL flying east to Honolulu, HI, you’d arrive in Honolulu yesterday, Friday, 5/3, because Honolulu is twenty-two hours behind Auckland. On the other hand, flying from Honolulu on Saturday, 5/4, to Auckland, you’d gain a day, arriving on Sunday, 5/6.

Recently, our N.Z. friends came for a visit. They experienced an extremely long Monday when they flew in. As days do, it began at 12:01 A.M. in N.Z. and ended at midnight in TX, which was 5 P.M. on Tuesday in N.Z. That amounts to a 41-hour-long Monday.

Did You Know…

• Tomorrow Island (Big Diomede Island, Russia) and Yesterday Island (Little Diomede Island, U.S.) are only two to three miles apart, but because the two islands are on opposite sides of the IDL, Tomorrow Island is almost one full day ahead of Yesterday.
• During the winter an ice bridge forms between Tomorrow and Yesterday Islands, but it is illegal to walk from one island to the other. That’s probably a good thing. Can you imagine asking a friend from the neighboring island to come to dinner? Depending on which direction the person travels, dinner might have been yesterday, or it might be tomorrow.

Phone Calls

Coordinating phone calls between Texas and N.Z. can be challenging. You don’t just pick up the phone and call. You have to think about what day and time it is at the other location. Currently, N.Z. is seventeen hours ahead of Texas. That means much of the time we’re in their yesterday and they’re in our tomorrow.

Many years ago, this concept of not really sharing a today led me to write the lyrics for a song I titled, Yesterday, Today, and Tomorrow. (Very imaginative, I know.) Unfortunately, the only recording I have is a duet I did with the friend who added the music. He set it in his key—too high for me—and we had no time to practice before we recorded it, so it’s far from polished. Still, I thought you might enjoy hearing it. (Click below to listen.)