The Light Cone Effect on the Shapiro Time Delay

We investigate the light-cone effect on the Shapiro time delay. The extratime delay caused by Jupiter on the 8th of September 2002 can be measured byadvanced VLBI (very long baseline interferometry). Our expression for the delayis in complete agreement with that of Kopeikin (2001), in which he argued thatthe excess time delay was due to the propagation of gravity. The presentletter, however, shows that the excess comes from nothing but the propagationof light, namely the light-cone effect. To make a robust confirmation ofgeneral relativity by the coming Jupiter event, it is important to take accountof the light-cone effect on the Shapiro time delay.Comment: 5 pages; accepted for publication in ApJ Letter