OK, mind blowing: A scientist at the Observatoire de Paris basically invented GPS for interstellar travelers: Simply tune in the radio signals from four pulsars, crunch some numbers having to do with relativity (natch) and read your position within the galaxy—to within a meter.
It makes sense. GPS is, after all, a system of satellites pulsing regular radio signals, which are triangulated by a receiver which must, even this close to earth, account for some relativity. Like the GPS satellites, the pulsars' locations are known, and also like the satellites, the pulsars pulse (hence the name) at known regular intervals, measured in milliseconds.
Bertolomé Coll and his associate Albert Tarantola determined that the point zero of the theoretical pulsar positioning system would be midnight on January 1, 2001, at the titillatingly named Interplanetary Scintillation Array in the UK, an homage, since this is the first radio telescope to pick up pulsars. Once you have the zero point locked in, your spaceship will know its whereabouts in space and time, and possibly how to steer clear of stars or asteroid fields when making that damned jump to hyperspace. [Technology Review; image from NASA]