Blue marble: The Earth captured by NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite.
Credit: NASA
BONN, Germany: In this high-tech age, you'd think we'd have the know-how to accurately measure the width of our planet, but researchers now reveal it's smaller than we thought.
Experts who took the last measurement five years ago, weren't that far out though – the difference is only half a centimetre.
German scientists from the University of Bonn took part in an international project to measure the diameter of the world and came up with the 5 mm decrease.
The scientists rounded the diameter of the Earth up to 12,756.274 kilometres (7,926.3812 miles) for the general public.
"Crucial difference"
Though it may appear a trifling difference, Axel Nothnagel, who led the 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," he said. "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 system of measurement used by the Bonn geodesists (geoscientists who study the size of the Earth) in the two-year project consisted of radiowaves that were 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 km."
The procedure is called Very Long Baseline Interferometry or VLBI. The technique can be used, for example, to demonstrate that Europe and North America are moving apart at a rate of about 18 mm a year.
The findings are reported in the Journal of Geodesy.
