Professor Shapiro's group will analyze the data from a 1987 very-long-baseline interferometry (VLBI) experiment to achieve a tenfold improvement in the accuracy of a classical test of general relativity: the deflection of light by the Sun. The interferometric data successfully recorded on 2-14 October 1987 consist primarily of observations of two radio sources: 3C279 and 3C273B, the former occulted by the Sun on October and the latter serving as a reference object. Signals were recorded in three widely-separated radio-frequency bands: 2, 8, and 23 GHz. Such frequency coverage will allow them to use the known dispersion relation for radio waves in the coronal and ionospheric plasmas to remove most of their effects from the observations. Auxiliary data will be used to account for the effects of the variations in Earth orientation, the brightness distributions of the two sources, and the Earth's neutral atmosphere. They expect to determine the deflection with a standard error of one part in 103 (i.e., to determine the parameter of the parameterized-post-Newtonian formalism to two parts in 103).
