What Is the International Date Line?
The International Date Line is an imaginary line of longitude on the Earth’s surface located at about 180 degrees east (or west) of the Greenwich Meridian. The imaginary dateline runs through the Pacific Ocean.
It marks the spot on the earth’s surface where each new calendar day begins. Because the earth rotates on its axis, the sun is always rising and setting someplace on earth, and the day is just beginning or ending.
To help keep dates straight in all parts of the world, it is necessary to have one place where we can note that the calendar day begins. The new date begins on the western side of the date line. As the earth turns, this new date sweeps westward around the earth.