The findings appear in the Sept. 25 issue of the journal Nature. They are part of a scientific collaboration between NASA and the Italian Space Agency. The experiment took place in the summer of 2002, when the spacecraft and Earth were on opposite sides of the Sun separated by a distance of more than 1 billion kilometres (approximately 621 million miles).

Researchers observed the frequency shift of radio waves to and from the spacecraft as the waves passed near the Sun. They precisely measured the change in the round-trip light time of the radio signal as it travelled close to the Sun. The round-trip light time is the time it takes the signal transmitted from the Deep Space Network station in Goldstone Calif., to the spacecraft on the other side of the Sun and back travelling at the speed of light.

"The scientific significance of these results is the important confirmation of the theory of general relativity and the agreement with Einstein's formulations to an unprecedented experimental accuracy," said Sami Asmar, manager of the Radio Science Group, which acquired the data for this experiment at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The technological significance of the experiment is the ability to overcome the harsh solar environment on radio links."… ...