In September 1522 the survivors of the Magellan and Elcano expedition, the first to circle the globe, reached the Cape Verde Islands with logs saying Wednesday, July 9, while locals said Thursday, July 10. Sailing west had cost them a day, as the 14th century geographer Abu’l-Fida had predicted. The International Date Line roughly follows the 180 degree meridian, but the 1884 International Meridian Conference in Washington, which set the prime meridian at Greenwich, refused to fix time zones or a date line, so the line has no treaty behind it and bends around national choices, swerving east around Russia’s Chukotka and passing between the Diomede Islands, 1.5 kilometers apart and 21 hours apart.

Kiribati, independent from the UK in 1979, straddled the line and shared only four business days a week until 1994, when it pushed the line east and created UTC+14, making one atoll, renamed Millennium Island, first to see 2000. With Baker Island at UTC minus 12, the clock now spans 26 hours, so three calendar days coexist for two hours daily. The Philippines, tied to Mexico by the Manila Acapulco galleons, stayed a day behind its Asian neighbors for over 300 years until it deleted Tuesday, December 31, 1844. Samoa repeated Monday, July 4, 1892 to align with American traders, then skipped Friday, December 30, 2011 to align with Australia and New Zealand.

• When Alaska passed from Russia to the US in 1867, it crossed the line and left the Julian calendar, so Friday, October 6 was followed by Friday, October 18.
• Many Seventh-day Adventists in Tonga keep the Sabbath on the local Sunday, and Samoa’s 2011 switch split its Adventist congregations.
• Islamic months begin with a physical sighting of the new crescent moon, sidestepping the line.
• Jewish refugees who reached Japan and China in World War II sparked debate over where a religious date line should fall.
• A 1917 Anglo-French conference set a rigid nautical date line, so a ship off Kiribati can sit in Sunday while the island is in Monday.