The International Date Line (IDL) is an imaginary line that runs along the surface of the earth from the North Pole to the South Pole in the middle of the Pacific Ocean and when you cross it you will win or lose a day depending on the direction of travel. If you go west you gain a day, and if you go east you lose a day.
For example, if a traveler travels across the Pacific Ocean from Wake Island to the Hawaiian Islands on June 25, they will jump back to June 24 as soon as they cross the IDL; However, if they travel in the opposite direction, they will reach Wake Island on June 26th.
Physics defies the magic that happens here. The international date line is based on a rational and practical universal timekeeping system that takes into account the movement of the earth around the sun.
Why do we need the international date line?
The earth rotates counterclockwise (from west to east). ) on its axis as it revolves around the sun. This means that different parts of the planet receive the direct rays of the sun at different times. So if it is noon on one part of the earth, the time when the sun is at the highest point in the sky, on another part of the planet it can be completely in shadow or experience sunrise or sunset.It also means that if you could somehow exceed the Earth’s rotation, which is a speed of around 1,600 km/h, you could, at least in theory, experience eternal daylight and never see darkness.
At such speeds (unless you are on the International Space Station) and when you are not traveling, people generally stay in one place so that people experience about the same amount of daylight, the day from sunrise.
The first time zone system was proposed by Sir Sandford Fleming in 1876, according to an article in Globe and Mail, a Canadian news publication. Canadian Railroad System he wanted to make the railroad more efficient and avoid complications resulting from the different timetables established by the various stations that set the time according to their local astronomical conditions. In encyclopedia Britannica, consequently, he proposed a system of 24 standard time zones, which would encompass the circumference of the earth Within each time zone, all clocks would be set to an average time that best reflects the position of the sun in the sky. The practicality of his system soon became popular, so in 1900 it was adopted by most of the world’s industrialized nations.
Today, with some major changes, we still use the 24-time zone system originally proposed by Fleming. The logic of dividing the earth into 24 zones arises from the fact that the planet is a sphere and, like any sphere, can be divided into 360 equal sections or 360 degrees, with each time zone being measured at 15 degrees latitude and 360 degrees divided. At 15 is 24.
All of these zones are numbered consecutively east from what is known as the Prime Meridian, a longitude that runs directly through the British Royal Observatory in Greenwich, Great Britain. The Prime Meridian was established in 1851 at a time when the United States was one of the most powerful and technologically advanced nations on earth. With a powerful navy, the British were very advanced in navigation and timing, using the most modern equipment available to calculate global position and time. The prime meridian at 0 degrees longitude is the point from which all other length measurements are made. The 24-hour timekeeping system called Greenwich Mean Time (GMT) is also located in the prime meridian.
As you move east from the prime meridian, the time zones increase continuously by an hour or, conversely, decrease continuously by an hour as you move west. But of course the earth does not exist indefinitely; At some point you will come to a point where, depending on the direction of travel, you have to start over or jump forwards or backwards in good time.
What happens when you cross the international date line?
Here is an example of how time zones and the international date line work.
London, U., is eight time zones away from San Francisco, California. When you drive from San Francisco to London, you are driving eight time zones forward, which really means you are eight hours ahead. So if it is 1:00 p.m. in San Francisco, it is 9:00 p.m. in London on the same day.
However, if you were to move eight time zones in the opposite direction at 1:00 p.m. from San Francisco. That means, west across the Pacific Ocean, for example to the Siberian city of Yakutsk, it gets complicated. Deducting Eight Hours from San Francisco Time You start by subtracting an hour for each time zone moving west and arriving at 9:00 AM. m., but at this point you reach the IDL where everything changes. add a full 24 hours to your calculations and skip a full day in advance so it’s 9 a.m.
Time because Yakutsk is four time zones west of the IDL. So when the time in San Francisco is 1:00 PM on wenesday. It’s 5:00 a.m. on Thursday in Yakutsk.
How the IDL began
The IDL was founded during the International Meridian Conference in Washington, D., in 1884, according to Post Card History. President Chester A. Arthur called the conference, attended by representatives from 26 nations. The President, like other world leaders, saw the need to set standards for an international agreement in terms of time and length. In the late 19th century, as global trade advanced, communication technologies became more sophisticated, and nations became increasingly interdependent, it was imperative that all watches conform to a world standard.
Against this background, the aim of the conference, as summarized in the minutes of the meeting, was “to establish a correct meridian”. used worldwide as the common zero for longitude and standard of time calculation models.
It is up to each country to implement these proposals. The IDL, for example, is still not a question of international law, nor is it enforced by the dictates of an international administrative council, it is accepted and adopted by all nations. because it is vital for global networking, instant communication, time tracking and consistent international databases.
Why isn’t the international date line straight?
A great way to visualize the IDL is to think in terms like a line of longitude. , roughly follows the 180 degree meridian, which is in the middle of the world, from the prime meridian. But in contrast to a meridian line, the IDL does not run on a straight path. Since its inception, the IDL has suffered several major deviations, and now it zigzags and trots around prominent land masses and certain Pacific islands in a seemingly arbitrary pattern. Most of these discrepancies are the result of practical considerations, such as avoiding splits by dividing a country into two time zones, or for political and economic reasons.
The IDL runs south from the North Pole, following the 180 degree meridian until it turns east to pass the Bering Strait, with Big Diomede Island, part of Russia, west of the IDL, and Little Diomede Island, part of. is, the United States remains in the east.Although the islands are only separated by the narrowest edge, only 3.2 kilometers, they experience different days, with Big Diomede Island always being one day before Little Diomede Island. The IDL then runs west to bypass the United States. “Aleutians keeping Russia and Alaska on opposite sides.
Then it goes back, following the 180-degree meridian again several thousand miles to the south, past the Hawaiian Islands to the west and the independent nation of the Marshall Islands to the Pacific island nation of Kiribati. East to include the islands of Kiribati and Line, the latter also known as the Teraina or Equatorial Islands. This deviation extends almost to the east to the 150-degree meridian and forms a very large and conspicuous hammer-shaped configuration.
Kiribati, received independence from the United Kingdom in 1979, it is a group of 33 largely uninhabited islands and atolls covering a vast area of no less than 1.9 million square miles (5 million square kilometers). its western half a day before its eastern half, according to the CIA’s World Fact Book. In 1995, Kiribati decided it had had enough of this agreement and, in search of better economic ties with Australia and New Zealand, expanded the IDL eastward. to encompass the nation’s far eastern islands, creating a strange configuration.
Changing the date line is relatively easy, the BBC reported. Neither the approval of other countries nor the sanctioning of an international umbrella organization is required.The country can decide for itself. It’s just a matter of spreading the word about the event and informing the international community and cartographers.
When leaving Kiribati, the IDL runs between Samoa and American Samoa, with the former being held in the west and the latter in the east of the IDL. it sharply returns to the 180 degree meridian but does not follow the exact course of the meridian, but instead remains parallel to the meridian and stays east of the line, so that Tonga, the Kermadec Islands, and New Zealand are all east of the IDL.
From New Zealand, near the Chatham Islands, which are part of New Zealand, the IDL goes back and reconnects with the 180 degree meridian, following this path until it reaches Antarctica, which has multiple time zones. in Antarctica on most maps.
Universal Coordinated Time
Today, a method known as Universal Coordinated Time, abbreviated as UTC, has become the standard for measuring time.In essence, it’s a more sophisticated version of GMT as it is still based on the zero degree of latitude that runs through Greenwich but is based on atomic clocks. Invented in the 1950s, these devices are incredibly accurate and rely solely on the rotation of the earth. Clocks account for minor fluctuations in the speed of the earth’s rotation that can cause normal time to fluctuate.
- Further reading: “Plotting the Globe: Stories of Meridians, Parallels, and the International Date Line (Explorations in World Maritime History)” (Praeger, 2005) by Avraham Ariel and Nora Ariel Berger
- Read more about the International Meridian Conference.
- Don’t feel like doing math? Here’s a helpful time zone converter that will do it for you.