Measurement of the Solar Gravitational Deflection of Radio Waves Using Very-Long-Baseline Interferometry

We made very-long-baseline-interferometry observations of the extragalactic radio sources 3C273B and 3C279 to measure the gravitational deflection of radio waves by the Sun. Cross-correlation of data recorded at antennas in California and Massachusetts at 2, 8, and 23 GHz during a ten-day period surrounding the October 1987 solar occultation of 3C279 yielded plasma-corrected group delays, from which we obtained $\gamma =0.9996\mathrm{}\pm 0.0017$ (estimated standard error), corresponding to a gravitational deflection $0.9998\pm 0.0008$ times that predicted by general relativity.