What is the name of the imaginary line where the date changes?

The imaginary line where the calendar date changes is called the International Date Line. It runs roughly from the North Pole to the South Pole through the Pacific Ocean, generally following the 180th meridian.

Crossing the line changes the calendar by one day. Travelers moving westward across it generally advance their date by 24 hours, while those traveling eastward set the date back by one day. This adjustment keeps calendar dates consistent with the worldwide system of time zones and Earth’s rotation.

The International Date Line is not a perfectly straight geographic boundary. It bends around countries and island groups so that communities, territories, and trading partners can remain on the same calendar day. Its course is a practical cartographic and political convention rather than a line established by a single international treaty.

The Prime Meridian is a frequent wrong answer because it is also an imaginary line, but it marks 0 degrees longitude through Greenwich, England, and serves as the starting point for measuring longitude. The International Date Line lies roughly opposite it, near 180 degrees longitude. Kiribati’s Line Islands, including Kiritimati, are among the first places to enter a new date.