Prime Meridian

geography · maps · Earth

Divides two worlds. The prime meridian splits Earth into the Eastern Hemisphere and Western Hemisphere, like an invisible line drawn through the planet from top to bottom.

Longitude starts here. All other lines of longitude are measured as degrees east or west from the prime meridian, making it the zero degree reference point for the whole world.

Not based on nature. Unlike the equator, which is determined by Earth's natural spinning motion, the prime meridian's location is completely made up by humans and could have been drawn anywhere.

Greenwich's legacy. The prime meridian used to pass through Greenwich, England, and most of the world agreed to use this location over a hundred years ago as the standard.

Modern refinement. Today's prime meridian is set by the IERS (International Earth Rotation Service) and is slightly different from Greenwich, making it even more accurate with help from satellites.