The International dateline.
When you cross the International Date Line, you move from one day to the next. This imaginary line on the Earth's surface marks the change in calendar days.
The Prime Meridian is an imaginary line that divides the Earth into Eastern and Western Hemispheres, but the day officially changes at the International Date Line, which is located approximately opposite the Prime Meridian. The International Date Line is where the calendar day officially changes.
When you cross the IDL, you turn your calendar one whole day, either forward or backward depending on what direction you're traveling. If you're traveling westward, with the US behind you and Japan in front of you, turn your calendar forward a day when you cross the line, and skip 24 hours. If you're traveling eastward, with China behind you and Canada in front of you, turn your calendar back a day when you cross the line, and repeat the previous 24 hours.
It is at midnight UTC on the International Date Line that the same calendar day is observed everywhere on Earth. At this point, the date changes from one day to the next for the entire planet simultaneously.
Becuase when you cross the Dateline, The time zone changes ahead because of how the hour changes 24 times in the world, It would be excaclty a day later. When you cross the Dateline It would be tomorrow, or yesterday. Whichever way you cross.
When crossing the line from west to east, you take the last page that you tore off of your calendar, and you glue it back on.
When the international date-line and midnight line up (once a day).
In that direction, you turn your calendar ahead 24 hours when you cross the line.
The Battle for Earth - 2010 Cross the Line 1-103 was released on: USA: 1 January 2012
Because when you cross it, you must change your calendar by one day, otherwise you will be out of sync with everyone else in the world.
the international date line
The International Date Line is an imaginary line on the Earth's surface that marks the change in calendar day. When you cross this line from east to west, you either add or subtract a day depending on the direction. It runs roughly along the 180° meridian in the Pacific Ocean.