Time Zone
timezone
A region of the globe that observes a uniform standard time for legal, commercial, and social purposes.
International Date Line
international date line
Overview
The International Date Line (IDL) is an imaginary boundary that runs approximately along the 180th meridian through the Pacific Ocean. Crossing it from west to east moves the date back by one day, while crossing from east to west advances the date by one day. The line is not defined by any international treaty and follows a zigzag path to accommodate the territorial boundaries of various nations.
Purpose
Time zones radiate east and west from UTC, accumulating a full 24-hour offset as they wrap around the globe. The Date Line serves as the reset point for this accumulated difference, ensuring that calendar dates remain logically consistent everywhere on Earth. Without it, a person traveling around the world would find their calendar one day out of sync upon returning to the starting point.
Notable Exceptions
In 1995, the Republic of Kiribati shifted the Date Line eastward to unify all of its islands under the same date, making the Line Islands (UTC+14) the first place on Earth to enter each new day. Samoa also moved to the western side of the line in 2011, reducing the business-day gap with Australia and New Zealand from nearly a full day to just a few hours.
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