Professor Shapiro's group will complete the analysis of their 1987 experiment to measure the deflection of radio waves due to the gravitational effects of the Sun. Using the technique of very-long-baseline interferometry, they observed two radio sources over a two-week interval centered on the annual passage of the Sun in front of one of the sources. By fitting this data with a model that includes a free parameter scaling the effects predicted by general relativity, they will determine the gravitational deflection with a standard error of 0.1 percent of the magnitude predicted by general relativity. Improving the accuracy of one of the few observational tests of general relativity is important not only as a test of the currently accepted theory of gravity, but also due to the role of general relativistic gravitation in the understanding of cosmology, black holes, quasars, and other massive astronomical objects. This "light"-deflection experiment is an advance over earlier ones since it uses signals recorded in three widely-separated radio-frequency bands (2, 8, and 23 GHz), allowing for higher accuracy corrections for the observational errors contributed by the dispersion of radio waves in the ionosphere and the solar corona.
