International Dateline

The International Date Line is an imaginary line of navigation roughly based on the meridian of 180° longitude 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.
The time difference between either side of the International Date Line is not always exactly 24 hours because of local time zone variations.
The Greenwich Meridian is a north-south line selected as the zero-reference line for astronomical observations.
The line in Greenwich in London, UK represents the world’s prime meridian – longitude zero degrees. Every place on Earth is measured in terms of its distance east or west from this line.