Greenwich Meridian, Geographic reference line at Royal Observatory in Greenwich, England
The Greenwich Meridian is the line of zero degrees longitude at the Royal Observatory in Greenwich, dividing the eastern and western hemispheres of Earth. This reference line runs from pole to pole through several countries and oceans, serving as a fixed point for mapping and navigation worldwide.
Representatives from 25 nations met at an international conference in 1884 and selected this line as the worldwide standard for measuring longitude. The decision also established the starting point for time zones, replacing earlier national systems that relied on different observatories.
Visitors often stand on a brass strip in the observatory courtyard and place one foot in the eastern hemisphere and the other in the western. Many take a photograph to mark this moment, turning it into a personal ritual of crossing an invisible boundary.
The physical marker lies in the observatory courtyard and is accessible during site opening hours. The location sits on a hilltop, so wear comfortable shoes and expect a slight climb if arriving on foot.
A green laser beam projects northward from the observatory roof at night, making the line visible in the sky above the city. This beam of light reaches over 20 kilometers (about 12 miles) on clear evenings, acting as a modern interpretation of the historical longitude reference.
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