Forgive me if this hs been asked before, I did a search but couldn’t find anything.
Say I design and build a starship capable of travelling throughout the galaxy as in Star Trek, how would I navigate back to Earth (or any other point)?
I assume that out to about 100 light years it would be possible to use radio emissions to direction find back to earth, but what about past that or to other planets without radio broadcasts?
I’d hate to get utterly lost on my ship’s maiden voyage.
I’ve been wondering this myself. Mostly after playing with Celestia a bit and then thinking ok where the hell am I and where is the sun!
Not sure looking out for radio transmissions would be much help. I imagine they’d be pretty tenuous that far out.
Here’s my idea: your starship has a map in its computer, a representation of the 3D space around the sun, for out to say ~500 light years. Compare the measured positions of all the dots of light you can see out the window, with all the positions stored in the map. A bit of pattern matching and… (waves hands) stuff… and you can work out where you are.
Yeah, I would think that you could use the stars to navigate pretty well, as long as you are prepared. Several bright stars in the Orion constellation - Rigel, betelgeuse, and the belt - are bright enough and far enough away that they’d still be close to each other and visible anywhere in our vicinity. Base on how offset the belt is compared to the other stars, and how much they still fall in a line, you’d be able to work out just how far you are to the side of earth with respect to Orion.
It would take a few other good reference points to be sure of things, I realize, but that’s the basic idea. Storing identifying information for bright stars would be very useful - spectral absorption patterns are like stellar fingerprints if I remember correctly, so that you’d be able to run the starlight from a blue supergiant through the computer and find out if it really is Deneb, for instance.
Oh, gosh, I was a bit too slow. What chrisk said!
At least, essentially. His statement is better than the more complex multi-step approach I would have used. But we were both thinking of the very luminous and relatively close Rigel. *
So here is the joke I was going to precede my analysis with.
Just find Neverland first.
Then take Peter Pan’s ** instructions (“Second star to the right and straight on 'till morning.”) and perform them in reverse! 
True Blue Jack
** The Wikipedia article on “Neverland” has a qualification on this and whether it is one word, two words, or two words with one or two additional “nevers” added.
I think this would be the way, actually, you wouldn’t even need to have a pre-existing map of anything. Just have the navigational computer map everything within a certain distance. It could calculate the distance to various stars in a 3D map as you went along. When it comes time to head back, you could go home the way you went. Or you could simply go a different way, as long as the computer could observe a few of the stars it saw on the way out you’d be fine.
Asimov dealt with this in a number of his stories. The idea was that your society has built up a map/database on the stars you can see, and recorded their spectra. Presumably, by locking on to and measuring the spectra of several bright stars, you can figure out which stars they are, and where you are in relation to them via triangulation. Of course, if you jump into the middle of a thick dust cloud, you’re screwed.
In Star Trek I always sort of assumed they had a virtual map of the galaxy and the computer, therefore, always knew the ship’s current location at least approximately. The virtual map wouldn’t have to register every star in the galaxy; just the important ones.
I would think one can use pulsars, which have a unique frequency as fixed points (or at least sort of fixed), and use them like we use GPS to navigate on earth.
You may wish to take a look at NASA’s little-known and very successful Deep Space 1 probe, which navigated itself with optical information.
Of course, it was a solar system probe, not sure if the same technique would be applicable to far interstellar travel.
There’s a really neat (at least to me) device on the market that can identify stars and other celestial objects merely by pointing directly at the object in question.
I’ve seen it advertised in various astronomy magazines, and its called the Meade mySky, and it retails for $399.00 (U.S.).
Could this maybe be the prototype for interstellar navigation systems?
I’m pretty sure the skyscout uses GPS.
The plaque on Pioneer and/or voyager used pulsars to show what planet/system they came from.
Brian
Using the system described so far, would you be able to communicate your position to another ship?
edit: D’oh… just read the above post.
The Voyage spacecraft included a map that showed the position of the Earth relative to a set of pulsars. That should be adequate within the galaxy.
Also, hopefully your starship would have the FTL equivalent of inertial navigation: the drive was engaged at xx% of maximum output for y amount of time while the ship was pointed in direction z. Accurate to maybe 1% of a light year, which should be close enough to the system you’re looking for. Of course that assumes a Star Trek-like warp drive. For jump drives, either you can directly calculate where your jump is going to, or else you have to rely on triangulation as said upthread.
The emission and absorption lines of notable bright stars, compared with their apparent magnitude versus absolute magnitude should allow for a positive ID of the stars themselves and their current distance from the ship, thus giving us a good position. The periods of the pulsars allows for a positive ID of individual pulsars, thus giving us another benchmark to measure against. Also, we have cepheid variables and the known nebulae (light and dark) to check against.
I wonder, tho, about intergalactic travel. Would our cepheid variables be enough to keep us on track? Super novas? Emission lines in the radio spectrum of active galactic nuclei? Let’s explore the galactic groups, the Great Wall, things like that, and then figure out how to come back home. Any ideas?
Just one thing to add: Once you figure out the starship drive, it would be a REALLY good idea to spend a bunch of time just working out parallax distance figures for distant stars by going about a light year or so and measuring them. That would enable the distances to be calculated much more precisely than we can do it here on Earth, which in turn would be of great value in using them to find your way home. 
Approximately? :dubious:
Guy, I wonder if you’ve watched every episode at least a dozen times as recommended.
For instance, in “Is there in Truth No Beauty?” Chekov does a double-take when he checks the ship’s position, after it has been shunted to some sort of offbeat subspace well outside the Galaxy, then navigated back by Spock-Kollos. (I must be getting old. It took almost a full minute to recall the title. 
) Still in virtual disbelief, he proclaims that the ship’s current position is so close to the position where it entered the warp “that the difference isn’t even worth mentioning.”
I was originally vague on just what that meant. Later I decided that the two positions would most likely overlap, at least a bit, in space. Upon reflection just now, I think it’s possible that he could have said the same thing if the nearest points had been within a couple-three ship-lengths or so.
The implication is that they could figure the ship’s position to within such a difference-not-worth-mentioning, if not an order of magnitude or two tighter.
True Blue Jack
Too bad they didn’t push Miranda down an open turbolift shaft.
But they still had to do some figuring. It wasn’t already set up for them in the computer.
My reasoning was that, based on the virtual map, the computer would “know” where they were in relation to Earth, Antares, and Betelgeuse, at all times. But it might not have sufficient data regarding all the little vicinities within that vast space
Trek has FTL sensors, so one could triangulate from the current position of some man made reference while inside explored space. The guy going further out would leave a buoy of some type much as Jack Aubrey would chart an unknown island and take navigation readings.