The 0° Meridian divides the Earth into East and West

The Prime Meridian of the World is called Greenwich because it passes through a city in England called like that.

The distance around the Earth measures 360 degrees, so there are 360 meridians: 180 to the East and 180 to the West. Each of them represents a degree of Longitude.

Longitude lines are a numerical way to show/measure how far a location is east or west of a universal vertical line called the Prime Meridian.

The Greenwich meridian also serves as the basis for the world's standard time zone system.

Every gain or loss of 1° longitude stands for 4 minutes. So add them when you move east of Greenwich Meridian or substract them when you move west of the G.M.

The Prime Meridian (Greenwich) divides the Earth into East/West from the North Pole to the South Pole with an imaginary line along the longitude line of 0°

This Prime Meridian line runs vertically, north and south, right over Greenwich in England, from the North Pole to the South Pole.

So, the meridians are vertical imaginary lines which divide the Earth in East and West hemispheres. The Prime Meridian is the Meridian 0°called Greenwich Meridional.