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Headed out from Earth within the Solar System, Sol and Earth both may be used as reference.

When traveling in interstellar space with stellar systems themselves traveling at varying velocities even within the Local Cloud; it probably gets even more discombobulating at the scale of the Bubble ... and beyond - How would one navigate?

Say, we developed interstellar travel and were able to send a probe on a round-trip to a neighbouring system. The probe wouldn't be able to rely upon a history of it's outward trip because the systems would have moved a little during the journey. The same would probably apply to a beacon because of the lag involved. What could one use as a navigation reference? Is there an interstellar map with system velocities and stuff maintained somewhere?

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You would use the stars as your reference. Of course, some stars are more suited to this than others. For example, the Voyager Golden Records had pulsar maps, that in theory some alien civilisation could use to locate Earth (what could possibly go wrong?). So, stars with unique and easily recognisable characteristics make good 'landmarks' (in particular, pulsars).

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  • $\begingroup$ Wouldn't their position change over time too? $\endgroup$
    – Everyone
    Jul 13 '12 at 4:01
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    $\begingroup$ @Everyone: I think you need to think a bit about the scale of things in these cases. How fast various stars are moving and how far away they are. Also consider that it will generally be possible to keep a constantly updating the database with fresh operations. Further, where do you want to go? If it is not to some visible (in some band) feature or to a spot defined in relation to such a feature I'd love to hear why. $\endgroup$ Jul 13 '12 at 4:21
  • $\begingroup$ @dmckee: There isn't a destination in mind just yet; it's merely a probable prerequisite for far space operations. A database update would also necessarily be limited to radio-speed; hence local. $\endgroup$
    – Everyone
    Aug 24 '12 at 8:02
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    $\begingroup$ The ship need not depend on database support from afar. They can carry their own instruments, and in any case on time scales less than many thousands of years you can get a very good approximation to the motion of the nearby objects before you leave. Nor will you pick just, say three stars to navigate by. You'll have a whole catalog of the buggers. Time and space scales matter, and your question seem to presuppose that things in the galaxy will move in a unpredictable way on time scales so fast that they can surprise the travelers. $\endgroup$ Aug 24 '12 at 14:55
  • $\begingroup$ Pulsars are only good for short distances and times. They switch off and their radiation is highly beamed and they move at hundreds of km/s. $\endgroup$
    – ProfRob
    Mar 30 at 7:24
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For interest, you could also use pulsars. I belive the idea here is that pulsars have unique and well-defined pulse times along with being bright, so you could use them as natural GPS satellites.

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  • $\begingroup$ The same pulsars aren't in general visible if you move to another part of the galaxy. $\endgroup$
    – ProfRob
    Mar 30 at 7:26
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One way to do this, is to develop a virtual dynamic map of the galaxy with all the correct positions and proper motions of the stars and nebulae. GAIA is the perfect source of this. Once you have a map, that is continually updating all the positions of the 100 billion stars, then navigating away or back to Sol shouldn't be too much of a problem. You can use Pulsars as landmarks, compare that to the same thing on the virtual galaxy map, n you know exactly where you are, and how to plot a course home or to whatever destination.

Without a map; you can't go anywhere n reliably get back in a system that is constantly in motion. It's like trying to sail from a boat on the sea, around the world and trying to get back to that boat with just a compass and no information on it's updated position.

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