What happens when you cross the International Date Line?
Quick Answer: When you cross the International Date Line going east, you subtract a day. Going west, you add a day. This keeps the calendar date consistent worldwide despite time zone changes.
The International Date Line is an imaginary line roughly along the 180° longitude. It acts as the "reset" point for calendar dates. When you cross it, your calendar date jumps forward or backward by one day.
This happens because the Earth is divided into time zones. Without the Date Line, the same moment could have two different dates depending on where you are. Crossing the line adjusts the date to keep things in sync globally.