After 131 years it turns out the Greenwich Meridian Line is in the WRONG place
Researchers have discovered the world famous stainless steel tourist attraction should not be at its current Royal Observatory location
People have been visiting it for decades but after 131 years it turns out the
Greenwich Meridian Line is in the wrong place.
Researchers have discovered the world famous stainless steel tourist attraction marking Longitude 0 should be in Greenwich Park – and not the Royal Observatory.
It should be 334 feet (or 102 metres) to the east of where the north-south line dividing the eastern and western hemispheres has been since 1884.
This was when countries met in Washington DC to recommend Earth’s prime meridian should pass through the Airy Transit Circle, a telescope for measuring star positions.
Named after Sir George Biddell Airy, the 7th Astronomer Royal, it tracked the movement of ‘clock stars’, stars which never rise or set.
Because these stars are always present in the sky and transit the meridian twice each day their appearance in the telescope cross hairs can be used to set time and longitude.
But modern navigators, mapmakers, surveyors and tourists have now got to get used to zero longitude being somewhere completely different.
Every place on Earth is measured in terms of its distance east or west from the Greenwich Meridian.
The line itself divides the eastern and western hemispheres of the Earth, just as the Equator divides the northern and southern hemispheres.
During the evenings, the position of the Meridian Line is often marked by a green laser in the sky.
Since the late 19th century, the Prime Meridian at Greenwich has served as the reference line for Greenwich Mean Time.
It claimed to be the centre of world time, and was the official starting point for the new Millennium.
But the superb accuracy of GPS receivers which uses satellites to precisely measure grid coordinates at any point on the Earth’s surface have replaced the traditional telescopic observations used to measure the planet’s rotation.
Astronomer Professor Ken Seidelmann, of the University of Virginia, said: “With the advancements in technology, the change in the prime meridian was inevitable.
“Perhaps a new marker should be installed in the Greenwich Park for the new prime meridian.”
Prof Seidelmann and his colleagues from the US Naval Observatory, the National Geospatial-Intelligence Agency and the US company Analytical Graphics Inc have been working to explain the situation.
The research published in the Journal of Geodesy shows the 102-metre mistake is down to the difference between two traditional ways of determining coordinates.
Because the Earth is not perfectly round, and because different locations on Earth have different terrain, these methods to measure longitude have built-in errors based on where they are taken.
A basin of mercury was used to make sure Airy’s telescope was kept exactly vertical so it could align with the clock stars.
But astronomers failed to take into account subtle changes in gravity would affect the telescope alignment and give a wonky reading.
Prof Seidelmann said GPS measures vertical from space in a straight line directly through the centre of the Earth, effectively removing the gravitational effects of mountains and other terrain.
At the 1884 meeting 25 nations awarded Greenwich the prize of Longitude 0 by a vote of 22 in favour to one against (San Domingo), with two abstentions (France and Brazil).
The USA had already chosen Greenwich as the basis for its own national time-zone system.
The decision, essentially, was based on the argument that by naming Greenwich as Longitude 0, it would inconvenience the least number of people.
Therefore, the Prime Meridian at Greenwich became the centre of world time, and the starting point of each new day, year and millennium.