Final answer:
The Prime Meridian is the imaginary line that divides the Earth into eastern and western hemispheres, running through Greenwich, England.
Step-by-step explanation:
The imaginary line that divides the Earth into the eastern and western hemisphere is the Prime Meridian. This line sits at 0 degrees longitude and runs through the Royal Observatory in Greenwich, England.
By placing one foot on either side of a marked band at this observatory, a person can stand in both the Eastern Hemisphere and the Western Hemisphere at the same time. The Prime Meridian is the point of reference for all other meridians or Lines of Longitude, which are numbered from 1 to 180 degrees east or west of this line.
While the Equator divides the Earth into northern and southern hemispheres, and the Tropic of Cancer and Tropic of Capricorn mark important latitudinal lines, it is only the Prime Meridian that separates the hemispheres into east and west.