Conventionally, the IDL is not drawn into Antarctica on most maps.(See § Cartographic practice and convention below.) A person who goes around the world from east to west (the same direction as Magellan's voyage) would gain or set their clock back one hour for every 15° of longitude crossed, and would gain 24 hours for one circuit of the globe from east to west if they did not compensate by setting their clock forward one day when they crossed the IDL.In contrast, a west-to-east circumnavigation of the globe loses an hour for every 15° of longitude crossed but gains back a day when crossing the IDL.
The International Date Line (IDL) is an imaginary line of navigation on the surface of the Earth that runs from the north pole to the south pole and demarcates the change of one calendar day to the next.
It passes through the middle of the Pacific Ocean, roughly following the 180° line of longitude but deviating to pass around some territories and island groups. (Times are approximate, since time zone boundaries generally do not exactly coincide with meridians.
Night and day is illustrative only; daylight hours depend on latitude and time of year.) The IDL is roughly based on the meridian of 180° longitude, roughly down the middle of the Pacific Ocean, and halfway around the world from the Greenwich meridian.
In many places, the IDL follows the 180° meridian exactly.
However, in other places, the IDL deviates east or west away from that meridian.
These various deviations generally accommodate the political and/or economic affiliations of the affected areas.
Proceeding from north to south, the first deviation of the IDL from 180° is to pass to the east of Wrangel Island and the Chukchi Peninsula, the easternmost part of Russian Siberia.
It then passes through the Bering Strait between the Diomede Islands at a distance of 1.5 kilometres (0.93 mi) from each island. It crosses between the Aleutian Islands, belonging to the US—Attu Island being the westernmost—and the Commander Islands belonging to Russia. Thus all of Russia is to the west of the IDL and all of the United States is to the east.
It then bends considerably west of 180°, passing west of St. The IDL remains on the 180° meridian until passing the equator.