The bright , nearby ( z=0.1685 ) gamma-ray burst of 29 March 2003 has presented us with the first opportunity to directly image the expansion of a GRB .
This burst reached flux density levels at centimeter wavelengths more than 50 times brighter than any previously studied event .
Here we present the results of a VLBI campaign using the VLBA , VLA , Green Bank , Effelsberg , Arecibo , and Westerbork telescopes that resolves the radio afterglow of GRB 030329 and constrains its rate of expansion .
The size of the afterglow is found to be \sim 0.07 mas ( 0.2 pc ) 25 days after the burst , and 0.17 mas ( 0.5 pc ) 83 days after the burst , indicating an average velocity of 3-5 c .
This expansion is consistent with expectations of the standard fireball model .
We measure the projected proper motion of GRB 030329 in the sky to < 0.3 mas in the 80 days following the burst .
In observations taken 52 days after the burst we detect an additional compact component at a distance from the main component of 0.28 \pm 
0.05 mas ( 0.80 pc ) .
The presence of this component is not expected from the standard model .