The Light-cone Effect on the Shapiro Time Delay

Abstract

We investigate the light-cone effect on the Shapiro time delay. The extra time delay caused by Jupiter on the 8th of September 2002 can be measured by advanced VLBI (very long baseline interferometry). Our expression for the delay is in complete agreement with that of Kopeikin (2001), in which he argued that the excess time delay was due to the propagation of gravity. The present letter, however, shows that the excess comes from nothing but the propagation of light, namely the light-cone effect. To make a robust confirmation of general relativity by the coming Jupiter event, it is important to take account of the light-cone effect on the Shapiro time delay.