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Galactic Positioning System

In 4 light years, turn left at Alpha Centauri
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As I understand it, quasars vary their output in regular ways, some over months and others over hours. Although they don't have atomic clocks, I suppose it's fair to say that they are consistent. So the known frequency of pulsation of all the known quasars, and the positions of them could be used to determine one's position in the galaxy.

Now that, I expect, might be very useful one day.

Ling, May 28 2009

From the Max Planck Institute... http://www.geek.com...spacecraft-2012042/
they're being original, about 3 years post-facto [lurch, Apr 02 2012]

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       If the method is mentioned at all, that is the way every SciFi book decribes it. (Apart from some weird constellation-recognizing techniques, that are humbug for pan-galactic navigation, but are used on deep space probes)
loonquawl, May 28 2009
  

       I'm not sure, but how far apart are quasars anyway? I think they might all be extra-galactic (i.e. in other galaxies far, far away) in which case, wouldn't they appear to be in the same place, and their signals arrive at the same time, no matter our position in the galaxy?   

       If you had an intra-galactic reference point (e.g. galactic central point) you could compare that with the quasar positions to get a bearing, but I'm not sure it would tell you how far 'in' you were from that centre.   

       It would be analogous to navigation by the stars - which, good though it is, definitely isn't GPS. You need objects that are more local, in Galactic terms (analogous to satellites)   

       [edit] Oops - I think we're getting confused between quasars and pulsars here (I know I am anyway). Quasars broadcast lots of energy, apparently omnidirectionally (which means that you can easily find them) but don't pulse regularly (which means that having found one, you can't be sure which one it is just by analysing the signal) Meanwhile Pulsars transmit lots of energy in a 'cone' that rotates lighthouse-like at very well defined intervals. They are also stellar rather than galactic, so we should be able to find plenty of them in our galaxy, assuming we know which way to look - that's good because you get the chance to sensibly triangulate. The downside here is that you might be in an area of the galaxy that's outside of your chosen pulsar's 'sweep' meaning you'd no longer be able to detect its signal.
zen_tom, May 28 2009
  

       The plaque on the Pioneer and Voyager space probes uses this idea to show Earth's location, but with 14 pulsars within our own galaxy. Pulsars are pretty consistent - although, over long periods, not as consistent as was once thought. Quasars, on the other hand, are not necessarily consistent.
lurch, May 28 2009
  
      
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