Here's why the Greenwich prime meridian 'changed'

The Greenwich prime meridian has changed and the scientists now explain it was expected all thanks to advanced technology.

In 1884, a delegation of international representatives convened in Washington, D.C. to recommend that Earth's prime meridian should pass through the Airy Transit Circle at the Royal Observatory in Greenwich, England.

But according to GPS receivers modern navigators, mapmakers, surveyors and London tourists now find that zero longitude runs 334 feet east of the telescope.

The reason is primarily the superb accuracy of the global positioning system, which uses satellites to precisely measure grid coordinates at any point on the Earth's surface - replaced the traditional telescopic observations used to measure the Earth's rotation.

Co-author and astronomer Ken Seidelmann at 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.

Seidelmann and his colleagues concluded that a slight deflection in the natural direction of gravity at Greenwich was responsible for the offset, along with the maintenance of continuity of astronomical time.

The research shows that the 102-meter offset can be attributed to the difference between two conventional methods of determining coordinates: astronomical versus geodetic, which refers to a set of reference points used to locate places on the Earth. Their difference is known as "deflection of the vertical," and high-resolution global gravitational models confirm that the east-west component of this deflection is of the proper sign and magnitude at Greenwich to account for the entire shift.

Meridian, he said, is dependent on the direction of the vertical, which is gravity- and observational-method-dependent. The distance and direction of the 102-meter offset is confirmed by gravitational models.

The paper is published in the Journal of Geodesy.