  We review our studies of spectator-induced electromagnetic (EM) effects on
the emission of charged mesons in the final state of ultrarelativistic heavy
ion collisions. We argue that these effects offer sensitivity to the distance
$d_E$ between the charged meson formation zone at freeze-out and the spectator
system. As such, they can serve as an independent, new tool to probe the
space-time and longitudinal evolution of the system created in the collision.
As a phenomenological application for this tool in the context of resonance
production and decay, we obtain a first estimate of the time of pion emission
from EM effects. This we compare to existing HBT data.
