Galactic GPS

Cool. When we travel the stars, we'll be able to know where we are. [Link]

Today, Bertolomé Coll at the Observatoire de Paris in France and a friend propose an interstellar GPS system that has the ability to determine the position of any point in the galaxy to within a metre.

Their idea is to tune in to the signals from four pulsars: 0751+1807 (3.5ms), 2322+2057 (4.8ms), 0711-6830 (5.5ms) and 1518+0205B (7.9ms), which each generate regular millisecond radio signals.

These form a rough tetrahedron centred on the Solar System.

Why four pulsars? Coll points out that on these scales relativity has to be taken into account when processing the signals and to do this, the protocol has to specify a position in space-time, which requires four signals.

Coll then defines the origin for this system of co-ordinates as 00:00 on 1 January 2001 at the focal point of the Interplanetary Scintillation Array, the radio telescope near Cambridge in the UK that first observed pulsars.