Greenwich Meridian line is actually 334 ft east...near a rubbish bin

For years visitors to the Royal Observatory have stood on the stainless steel Greenwich Meridian Line believing they are located exactly between east and west and at the centre of world time.

But anyone curious enough to check their positioning using GPS might have spotted an unfortunate discrepancy …it’s not actually at 0 degrees longitude.

The Prime Meridian, the imaginary line which runs from the North Pole to the South Pole, is actually 334 feet to the east, cutting unceremoniously through a footpath, not far from a rubbish bin.

Now scientists have explained how the error occurred. Earth-bound astronomers who calculated the original line did not take into account distortions caused by gravity when aiming their telescopes at the so-called ‘clock stars’. However satellites for global positioning systems make minute adjustments for the effect. So when GPS was switched on in 1984, the real prime meridian was revealed.

“With the advances in technology, the change in the Prime Meridian was inevitable,” said Ken Siedelmann, an astronomer at the University of Virginia and co-author of the study published in the Journal of Geodesy.

“Perhaps a new marker should be installed in the Greenwich Park for the new Prime Meridian."

The Royal Observatory’s public astronomer Dr Marek Kukula told The Independent that he was frequently asked by puzzled members of the public why their GPS did not align with the meridian.

“We’re forever telling this story, making the point that as we refine our measurements and get better technology of course these things change, because we want to have the best possible data,” he said.

“I think having a marker in the park would be brilliant to update the story of the Greenwich Meridian into the 21st Century. At the moment, the nearest thing there is to a marker is a litter bin.”

To confuse matters further, there are already two other meridian lines at Greenwich, the Halley Meridian and Bradley Meridian, which were used before the current marker.

The Prime Meridian was set in 1884 using the large Transit Circle telescope built by Sir George Biddell Airy, the 7th Astronomer Royal. The telescopes tracked the movement of ‘clock stars’ – circumpolar 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.

A basin of mercury was used to make sure that Airy’s telescope was kept exactly vertical so that it could align with the clock stars. But astronomers failed to take into account that subtle changes in gravity would impact the telescope alignment and give a wonky reading.

The Greenwich Meridian was chosen to be the Prime Meridian of the World in 1884.

Forty-one delegates from 25 nations met in Washington DC for the International Meridian Conference. By the end of the conference, Greenwich had won the prize of Longitude 0º 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 and at the time, 72 per cent of the world's commerce depended on sea-charts which used Greenwich as the Prime Meridian.

The decision, essentially, was based on the argument that by naming Greenwich as Longitude 0º, 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.