Greenwich is a place in England. If you look at a map, places to the left are west of Greenwich and places to the right are east. A meridian is any line which runs from north pole to south pole and...
The Prime Meridian is the imaginary line that joins the earth's north and south poles and crosses a groove in the floor of the Transit Room of the Royal Observatory in Greenwich, England. By...
The antimeridian, at longitude 180° (West/East).The International Dateline is not the same thing, it skirts several areas to make time zones work better, and so doesn't have a consistent longitude.