Measurement of Aberration of Gravity Using Jupiter's Motion

On September 8, 2002 Jupiter passed within 3.7 min of the bright radio source, J0842+1835. The deflection predicted by General Relativity (GR) of this source at closest approach contains two major terms: an outward radial deflection from Jupiter of 1190 arcsec, and a deflection of 51 arcsec associated with the aberration of gravity. We used the Very Long Baseline Array with the Effelsberg telescope to measure the position of J0842+1835 with respect to two quasars a few degrees away during the period of September 4-12. With the use of two quasars on opposites sides of the radio source, we removed most of the tropospheric delay variations, and obtained the deflection of J0842+1835 on September 8 to an accuracy less than 10 arcsec. The aberrational part of the deflection that we measured is 0.98 +/- 0.19 times that predicted by GR. The speed of gravity associated with the measured aberration of the gravitational field of Jupiter is (1.06 +\- 0.21) times the speed of light.