<P> 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 IDL must therefore be observed in conjunction with the Earth's time zones: on crossing it in either direction, the calendar date is adjusted by one day . </P> <P> For the two hours between 10: 00 and 11: 59 UTC each day, three different calendar dates are observed at the same time in different places on Earth . For example, at 10: 15 UTC Thursday, it is 23: 15 Wednesday in American Samoa (UTC − 11), Thursday in most of the world, and 00: 15 Friday in Kiritimati (UTC + 14). </P> <P> During the first hour (UTC 10: 00--10: 59), all three calendar dates include inhabited places . During the second hour (UTC 11: 00--11: 59) one of the calendar dates is limited to an uninhabited maritime time zone twelve hours behind UTC (UTC − 12). </P> <P> According to the clock, the first areas to experience a new day and a New Year are islands that use UTC + 14 . These include portions of the Republic of Kiribati, including Millennium Island in the Line Islands, as well as Samoa during the southern summer . The first major cities to experience a new day are Auckland and Wellington, New Zealand (UTC + 12; UTC + 13 with daylight saving time). </P>

Where does each day begin in the world