How would one navigate interstellar space? 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?
 A: 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).
A: 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.
A: 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.
