Which line of longitude passes through the Royal Observatory in Greenwich, London?

The Prime Meridian is the line of longitude that passes through the Royal Observatory in Greenwich, London.

It represents 0 degrees longitude and serves as the reference from which east and west longitudes are measured. The modern internationally recognized meridian follows a line slightly east of the historic telescope-based line at Greenwich because satellite-based geodesy uses Earth’s centre of mass.

Greenwich became the international reference after the 1884 International Meridian Conference in Washington, D.C. The choice reflected the widespread use of British nautical charts, many of which already used the Greenwich meridian.

The Prime Meridian is different from the International Date Line. The Prime Meridian is the starting reference for longitude, while the Date Line lies roughly 180 degrees away and marks a change in calendar date. The Equator, by contrast, is a line of latitude dividing the Northern and Southern Hemispheres.