Can tell a ship hasn't left the star system

Vader turned to Tarkin. “We sidestepped the smaller trap only to fall into the larger one, Governor. If nothing else, we now know the reason we were lured here.” Bringing his left hand to the brow of his helmet, he paced away from Tarkin and the ambassador, then swung back to them. “The ship is still in the Murkhana system.”

Tarkin didn’t waste time asking how Vader knew that to be the case.

- Tarkin, Chapter Eleven, Page 201