Why Greenwich Became the Prime Meridian: The Story of Longitude and the Royal Observatory

The historic observatory at Greenwich is now a museum, but how did it get to be the historic Prime Meridian (the zero longitude line that divides the Earth into eastern and western hemispheres for navigation) of the world?  Why a relatively obscure place in South London?  This animated short, created by the Royal Observatory, delves into its history and explains these and other questions getting a little existential – why does it even exist at all? It all boils down to longitude – the measurement of position east or west of the Prime Meridian, used to locate places on Earth accurately - and the need to calculate it using the moon and the stars.  There was a very good reason for this - accurate navigation at sea and preventing ships from getting lost, not to mention speeding up journey time. This depended on knowing precise longitude for safe global trade and travel.

As a quick aside, many people assume that the Royal Observatory in Greenwich is still an active astronomical research site, but this isn’t the case. The Observatory stopped being a working research facility in Greenwich in the mid-20th century, when its scientific work was moved elsewhere in the UK, including to Herstmonceux in Sussex and later into institutions connected with Cambridge. Today, the Greenwich site mainly serves as a museum and public attraction.

Modern UK-based observational astronomy often makes use of large international observatories in places such as the Canary Islands, where conditions are much better for stargazing, but these facilities are not a continuation of the Royal Observatory itself.  Aside over (not as quick as I anticipated), watch the fascinating video below.