Small World

Five millimeters (0.2 inches) is less than half the width of an average finger and seems negligible when compared to the earth's diameter of 12,756.274 kilometers (7,926.3812 miles). But German researchers, who participated in an international project, have now found that the globe's exactly five millimeters "thinner" than originally expected.

They said the difference is crucial when it comes to studying climate change.

"It is essential for the positioning of the satellites that can measure rises in sea level," Axel Nothnagel, who led the team of researchers in Bonn, told AFP news service. "If the ground stations tracking the satellites are not accurate to the millimeter, then the satellites cannot be accurate, either."

Measuring radio waves

Nothnagel's team worked two years on the project and used radiowaves to measure the earth's diameter.

"A network of more than 70 radio telescopes worldwide receives these waves," Nothnagel said. "Because the gauging stations are so far apart from each other, the radio signals are received with a slight timelag. From this difference we can measure the distance between the radio telescopes to the preciseness of two millimetres per 1,000 kilometers."

The procedure is called VLBI, which stands for "Very Long Baseline Interferometry". The technique has also been used to show that Europe and North America are moving apart at a rate of about 18 millimeters a year.