What Ocean Does the International Date Line Run Through?

February 15, 2024

The International Date Line is the dividing point between two calendar days. It's located halfway around the globe from the prime meridian (zero degrees longitude) established in Greenwich, England. The line is a little different than the Greenwich meridian though, and that's because it runs through the middle of the Pacific Ocean and doesn't stop at any land masses. The line zigzags here and there to avoid splitting countries into different days, like it does around Kiribati, the nation of 33 islands that straddles the equator.

At the International Meridian Conference held in 1884, 26 countries agreed to create an imaginary line that would separate one day from another. It was decided to use the Pacific Ocean because it was largely an open ocean and not a land mass, but it was also determined that the line should not be connected with any other meridian lines. Instead, the IDL was chosen as an arbitrary line that stretches north to south through the center of the Pacific and reaches east to west from its beginning in Greenwich.

Since its inception, the IDL has shifted a few times to accommodate the needs of countries near it. The most prominent zigzag occurs in the Central Pacific, where the IDL swerves to keep Samoa and Christmas Island celebrating a new day first, then bends to skirt the Bering Strait to keep Big Diomede Island, Russia, and Little Diomede Island, Alaska, on separate days. It jogs back to connect with the 180-degree meridian just south of New Zealand's Kermadec Islands and Chatham Islands, but it doesn't extend into Antarctica because that region has multiple time zones.

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