They’d already done that to Ann Mulhall and trying to explain two incidents was too risky.
Using spectral data to “fingerprint” stars might not be such a great idea, with FTL technology. The spectrum of a star will change over its lifespan, and the brightest stars have the shortest lifespan. When you’re very close to a star, you’ll be seeing its spectrum as it is now, or close to it, but when you’re a million lightyears from a star, you’ll see its spectrum as it was a million lightyears ago.
Enough of that; what would I do? For the sake of this discussion, I’ll assume that I have just invented a jump-drive and am testing it. I know it’ll jump me to someplace else, but I have no idea how far, and I’m not even close to developing a “dead reckoning” system.
The first thing I would do is find as many quasars as I can in the sky. If the arrangement is a reasonable approximation of their arrangement as seen from Earth, then I can first of all figure out what direction is which, and then by the way their arrangement is perturbed from Earth-normal, I can calculate an approximate position. Using this approximate position, I then figure out what major galaxies should be nearby, and compare them to the nearby galaxies I can observe. If I’m in a galaxy, and it’s one realtively close to us, I’ll have a database of its globular clusters, and I can further refine my position from that, and so on with nebulae and bright stars. At a rough order of magnitude guess, I think I could determine my position this way to within an error of about 10[sup]-6[/sup] of my distance from Earth (that is, if I were a million lightyears from Earth, I could determine my position to within one lightyear, and so on).
If my initial quasar search comes up dry (I can’t recognize any sort of pattern at all), then things get a bit tougher. My next step then is to do a complete-sky map of the Cosmic Microwave Background, and compare it with the data from the MAP satellite (or whatever better equivalent is available). I then run a brute-force search looking for matching circles in the two datasets. If I find such a circle, then I know that home is in the direction of the center of that circle, and the size of the circle tells me approximately how far away I am. If the circle is large enough, I might look for quasars within it, and use my additional information to try to match them again to quasars known from Earth, and further refine my results that way. With or without the quasars, though, I’m probably not going to get results much better than 1% (unless the technology is much better than currently).
And finally, if I can’t even find any matching circles in the cosmic microwave background, then I’m well and truly lost. All I can do, even in theory, is put a lower bound on my distance from Earth. I could be 100 billion lightyears away; I could be a googol lightyears away.
As the self-appointed representative of the cosmological ignoramuses (ignorami?) around here, could you briefly explain how you can be 100 billion light years away in a universe where the maximum dimension is around 15 billion light years? Thanks!
Not to mention the POSITIONS of the starts change. You’ll always be seing their position as they were depending on your distance from them. Sure it might not matter if your stick to your neighborhood within 100 or so light years, but I imagine the error might be significant as you get into 1000s or 10s of 1000s of light years away. Kind of like navigating to a bouy that’s in a diferent position depending on how far away from it you are.
That’s just the universe we can observe. Who knows what, if anything, might be 100 billion light years past that?
…is the star tracker. ICBMs, imagery satellites, and high-altitude aircraft use star trackers to get an optical fix on five or six stars and can use that data to find their pointing angle to a very high precision. I’m pretty sure you can also use them to get position information. Combining a slowly-updating sensor like a star tracker with GPS, integrating accelerometers, and good gyroscopes can give you a nearly continuous stream of position data.
So, chronos (and others), what about the cepheid variables? Their absolute magnitude and period are linked, right? Would they make a decent benchmark/signpost/landmark?
Won’t their position have shifted over time too?
Not only their positions, but their status as cepheids. A cepheid isn’t so much a special kind of star, as a special time during a star’s life sequence. Over a relatively short time span, a star can evolve into a cepheid, and then evolve back out of being a cepheid. There are even some stars which have ceased being cepheids in the time since we’ve been observing them.
From any given point in space, I’ll be able to find some cepheids, and I’ll also be able to determine how far away they are. But they probably wouldn’t be the same cepheids we see from Earth.
One thing to consider is that, even if you get really and truly lost on your first jump, as long as you can maybe learn to calibrate your jump drive while you’re out there, you can always use some kind of three-dimensional spiraling-outward search to do a controlled search for something you’re trying to get back to. Assuming that the univers isn’t infinite (or, at least, that you have a realistic upper bound to the distance you could have traveled on your first jump), then it shouldn’t take too long to get back to where you started from.
Even a 3-Dimensional random walk will give you better than one chance in three of returning to your starting point.
The age of the universe and the size of the universe are not the same thing.
The universe, while estimated to be around 15 billion years old, is also estimated to be possibly around 156billion light years wide.
The expansion of the universe at some points in it’s history has exceeded the speed of light (which doesn’t violate any of Einstein’s “guidelines”).
I’m under the impression that everything in the universe is in orbit around something else in the universe, so pointing your FTL ship at someplace is a silly way of getting there. Don’t you have to basically change your current orbit around whatever it is you’re orbiting, to a new orbit around where ever it is you want to go? I mean, pointing your ship at Betelgeuse and jumping in a straight line there isn’t going to get you anywhere near Betelgeuse, right?
I don’t think it’s too bad. Betelgeuse may be orbiting the center of the galaxy, and also drifting relative to other stars in its area, but compared to the kind of speed you’ll need to arrive at Betelgeuse in less than 8 years or so, that effect isn’t very great. You can just point at the star you see and course-correct every 20 light years or so.
It’s within a star system that orbital speeds get high enough (relative to the distances involved) that you need to match orbits and not just point at what you want to land on.
Never underestimate the power of a good nursery rhyme. For instance:
“Set your course by the old Dog Star
A point to the north of Achernar;
Fare until on the starboard beam
Six red suns towards a blue sun stream.
Sleight your ship to where afar
A cluster hangs like a scimitar -
Under the hilt to the verge extreme
And dead ahead shines Thamber’s gleam”
worked well enough for… bonus geek points, anyone? 
That’s an idealized situation where the walk and the positions it covers are in discrete units. If your random walk spans the width of the galaxy, it might take you “nearly” back to your starting point, (where “nearly” is ~500 light years) in less than the lifetime of the crew.
Kirth Gersen, tracking down Kokkor Hekkus in Jack Vance’s The Killing Machine! Which co-incidentally I re-read a few days ago…
/me hands matt a cigar. 
Okay, I see what you mean.
True Blue Jack
MapQuest
It’ll even print out the map for you.
Sheesh - some people overthink everything