BONN, July 5: The world is smaller than first thought, German researchers at the University of Bonn said on Thursday. They took part in an international project to measure the diameter of the world that showed it is five millimetres (0.2 inches) smaller than the last measurement made five years ago.

Dr Axel Nothnagel, who led the Bonn researchers, said the difference was crucial in the study of climate change.

“It may seem a very small difference, but it is essential for the positioning of the satellites that can measure rises in sea level.

“They must be accurate to the millimetre. If the ground stations tracking the satellites are not accurate to the millimetre, then the satellites cannot be accurate either.” The scientists round the number up to 12,756.274 kilometres for the general public.

The system of measurement used by the Bonn geodesists in the two-year project consists of radiowaves that are transmitted into space.

“A network of more than 70 radio telescopes worldwide receives these waves.

Because the gauging stations are so far apart from each other, the radio signals are received with a slight timelag,” Nothnagel said.

“From this difference we can measure the distance between the radio telescopes to the preciseness of two millimetres per 1,000 kilometres.” The procedure is called VLBI, which stands for “Very Long Baseline Interferometry”. The technique can be used, for example, to demonstrate that Europe and North America are moving apart at a rate of about 18 millimetres a year.

—AFP