International Date Line: Concept and Places it Passes Through

International Date Line is an imaginary line on the surface of the Earth which demarcates change of a calendar day. It is the anti-meridian or 180th meridian of the modern Prime Meridian passing through Greenwich.

Why International Date Line is not Straight?

International Date Line is inconsistent unlike other meridians of longitude. It runs in a zigzag fashion at some places to avoid passing through a country. From the North Pole, date line first deviates eastward through the Bering Strait to evade the division of Siberia. It further deviates slightly west to group Aleutian Islands with Alaska. In the Southern Hemisphere, it again deviates in the eastward direction so that the calendar date is same in entire New Zealand.

Date Change on crossing the International Date Line

One calendar day is lost while crossing the International Date Line from west to east. Whereas crossing the International Date Line, from east to west, there would be a gain of one calendar day. For example, let’s assume someone from Alaska leaves for Japan on 10th May. As soon as he crosses the International Date Line, the calendar date will change to 11th May. It will be like the person has suddenly transmitted into the future! Hence, he will lose one whole day.

Difference between de facto Date Line and de jure Date Line?

International Date Line is a globally accepted standard but it has no sanction under the International Law. Hence, the International Date Line is also called de facto date line. All countries of the world determined their standard time zones applicable to exclusively to their territory including land and territorial waters. However this was applicable nationally and there was no international law to determine the time zone for international waters.
Thus by virtue of an international agreement, the concept of nautical date line came into existence. This date line is de jure. Unlike international date line, nautical date line follows the 180° meridian except where it is interrupted by territorial waters adjacent to land, forming gaps.

How does Navigation Takes Place?

There are broadly two possibilities of navigation — either the ship is sailing in international waters or through the territory of any country. Hence, if the ship is sailing through territorial waters of any country, the standard time of the country is adopted. Similarly, once the ship leaves territorial waters and enters international waters, it starts following the international time zones.

A Few Questions Related with International Date Line

Which Ocean does the International Date Line Pass through?

The International dateline passes through the Pacific ocean. From the North Pole to the South Pole, it roughly runs through the middle of the Pacific ocean.

Which Strait does the International Date Line Pass through?

The International Date Line passes through Bering Strait that separates Russia and the United States.

Which Countries does the International Date Line Pass through?

The International Date Line does not pass through any nation. It passes roughly through the mid-pacific ocean. This has been done considering that the date changes on crossing the date line. Had the International Date Line crossed land of any country, it would have caused confusion as the eastern part of the country towards Japan separated by the date line would have been a calendar day ahead of the western part towards North America. This is also precisely the reason why the International date line is zigzag. By maintaining a zigzag line, it has ensured that it does not cross any country or prominent landmass.

When was the International Date Line Established?

The International Date Line was established in the year 1884.