Dependent on light, sensors cannot detect objects moving at a faster-than-light speeds. No ship can be detected at interstellar ranges. Detection at interplanetary ranges suffers from light speed lag: observers see ships not where they appear to be but where they were when the light bearing their image left them, minutes, hours, or days before. To counteract light speed lag, battle fleets surround themselves with spheres of screen and scouting frigates.
Pursuers cannot detect ships and directly intercept them. Instead, pursuers track where objects were, where they were heading, and at what speed they were moving. Such data reliably predicts an object's future location and for pursuit along its light-lagged "wake". Ships trying to evade pursuit follow erratic zigzag courses, requiring pursuers to make stops to update their projections.