Was thinking of Planet of the Apes and them not realizing that they just returned to Earth in the future. Say you need to know where you are, and hence where Earth is, and thus which direction to head off on to get back (assume your vessel has Trek-style warp drive).
If the other system in question is nearby it can probably be a cinch, just note the modest type F star in a constellation that normally doesn’t have such, and where Sirius and Vega and Alpha Centauri are at now, and that assumes you cannot ID the star you are in orbit around.
A lot depends on how much data you have-Sirius’ spectrum and white dwarf companion could probably help identify her without too much trouble.
5,000 light years away, and you would presumably have a lot more trouble. Orion Nebula? Eta Carinae? Deneb? Various globular clusters would probably be your best bet.
What if however you are on the other side of the galaxy? Then you would need M-31, M-33, and probably most Magellanic Clouds, assuming they aren’t all blocked by the Milky Way itself.
Was already thinking of starting this topic when I spied this post by @LSLGuy about navigating on the moon vis a vis where Earth is:
The Pioneer craft should Earth’s location relative to 14 pulsars. They differ in frequency. So if you could receive a few of those radio signals, I’d think you could locate the solar system.
Great thought. Pulsars are (probably) the distinctive landmarks you want. Rare, but not too rare, and each distinct enough to pretty well unambiguously identify.
In addition to where you are in the galaxy = near or far from Sol & Earth, it also depends hugely on when you are. 500 non-relativistic Earth years after you left, 5,000, or 500,000?
In addition to the galactic orbit all the stars move around in, there’s the “proper motion” of each of them versus the average galactic revolution in their neighborhood. Some stars are really zipping along versus their neighbors and others are just moseying along with the herd.
If you knew how much non-relativistic time had passed, given good enough star data to begin with, you could fast-forward your maps to your now-current era and look around for landmark-type stars. If you don’t know how long it’s been, you could try matching what landmarks you can find to maps at varying degrees of fast-forward until you get a decent match. At that point you’ll know roughly when you are.
Of course if your maps / data don’t have that much detail on most stars & pulsars, you’re screwed. That was bad mission planning / prep.
Not sure how good pulsars would be. It’s true they each have a specific frequency, but that frequency is not fixed. They are all gradually slowing down. But then along comes a starquake and the frequency goes back up by some non-predictable amount.
Well you find 7 or 8 of them plot the lines and ignore the 1 or 2 that see off, but the chances are if the frequency changed a lot, you wouldn’t even recognize it as one of your targets.
If your spacecraft’s nav package is able to see the cosmic background radiation, you could align it to determine what direction you are pointing. then look at the galactic center for distance and parallax against the background. This would, depending on the accuracy of your instruments, tell you where you missed the I-5/I-405 interchange and get you back to the solar system.
Pulsars wouldn’t work. They’re directional. You can only pick up the pulses from a pulsar if you’re right on the double cone its beam sweeps across.
If you know you’re in the Milky Way Galaxy, then your first step is to find the center of the Galaxy, the Andromeda Galaxy, and the Magellanic Clouds. All of that is easy: You can get the rough center of the Galaxy easily with the naked eye, and the exact center will usually be the brightest thing in the sky in radio. And the other galaxies are also all naked-eye. Those would be enough to get a rough position, that you could then fine-tune with globular clusters.
If you don’t even know what galaxy you’re in, then it gets harder. You start by looking at the cosmic microwave background, and whatever quasars you can see. If the CMB is roughly right, then you look for quasars and large galaxy clusters, and maybe from there individual galaxies. If the CMB doesn’t look even roughly right, then you spend a whole bunch of computer time (several weeks on a large computing cluster last I saw, but that was a couple of decades ago) looking for matching circles between the CMB you see and the one we know. If you can’t even get any matching circles, then you’re out in the Great Beyond and well and truly lost.
Overall, I’d roughly estimate that using current astronomical data and observational capabilities, at any distance up to twice the radius of the observable universe, you could get your position with a precision of about 5% of your distance from Earth. Of course, if we had the capability for interstellar or intergalactic travel, we’d very quickly build up much better astronomical databases that could be used for much more precise positioning.