Galactic GPS?

The Global Positioning System, GPS, works by comparing the delay in signals received from clocks located in different places - specifically on satellites orbiting the Earth. The most accurate clocks in the universe are these, but millisecond pulsars - notable for the regular pulses of radio emission ~1 ms apart and their gamma-ray emission. Using data from the Fermi telescope, astronomer identified some possible milli-second pulsars which were then confirmed using radio observations. Now, they are being monitored not to determine the location of Earth in the Milky Way, but to see if they are correlated changes in the arrival time of their radio pulsars which might indicate the passage of a gravitational wave passing between us and them. Go here for more information. Enjoy!