Answer:
The Prime Meridian
Explanation:
Meridians are imaginary lines that form a circle around the sphere of the Earth. They pass both through the north and south pole and divide the Earth into what we know as time zones. The Prime Meridian is located at longitude 0 degrees, so it divides the sphere of Earth into two halves, known as hemispheres. Using cardinal points, we can call them Eastern and Western Hemisphere. The exact location of the Prime Meridian was first established in 1884, and it passed through the Greenwich observatory in Great Britain. Later, in 1973 it was moved slightly since new technologies were introduced that allowed to place the Prime Meridian exactly over the center of mass of the Earth.
