There is a line in the Pacific where you can step into tomorrow. Cross the international date line going west and the calendar jumps a day ahead; cross back and you have, in a sense, gone back in time. Yet the line has no legal international status at all.
The international date line, shown here in yellow, marks the boundary between calendar dates. Credit: NOAA.
Where it runs
Established in 1884, the international date line passes through the middle of the Pacific Ocean and roughly follows the 180 degrees longitude line from north to south. That puts it halfway around the world from the prime meridian — the 0 degrees longitude line at Greenwich, England.
What it does
The date line is a "line of demarcation" between two consecutive calendar dates. West of it, it is one day later than east of it.
A line that bends
Despite its name, the international date line has no legal international status, and countries are free to choose which date they observe. It runs generally from pole to pole, but it zigzags around political borders — around eastern Russia, for example, and Alaska's Aleutian Islands.
Sources
Based on "What is the international date line?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
许可协议： CC0 1.0（公有领域） · 改编自 oceanservice.noaa.gov
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