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Average Joe was an amateur astronomer. While he was out in the wilds one day with his telescope he was kidnapped by aliens, carried off and kept as a slave on a world somewhere in the Milky Way. Having learned enough of their language and technology to steal a ship he now needs to find his way home.

The ship is powered by narrativium and travels at the speed of plot, it's guaranteed to get him home before his dog dies as long as he points it in the right direction.

What knowledge could Joe have that would allow him to find his way home, or is he lost forever?

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That will not be easy. Our galaxy is about 100 000 ly across and you can see Sun with naked eye at 80 ly at best. Of course you can see a lot further with a telescope but there are 4–16 billions of yellow stars, that would look like Sun from afar.

But it would be possible if we postulate perfect memory of Joe(or all necessary data saved on his laptop) and ability to do as much as hyperjumps as we need for any distance in a short time.

As it was already mentioned you can narrow the area with image of the galaxy.

Galaxy and Sun

But that would not be enough. As you go somewhere around that part of Orion Arm you still will be thousands ly from the Sun and there would be millions of stars around.

You will need to look for extremely bright stars - above 100 000 of Sun's luminosity. A star like that would be one of the brightest stars on the sky even when seen from several thousands ly. If you do several 100 ly jumps you will see that most bright stars will go bleak and only our candidate will "move" with us.

We can find only several stars like this several thousands ly around, some of them would be Deneb, Aludra or some other star from the list of brightest stars(look for the distant ones on this list).

Now we can start to look at colors of those stars and distances between them. By doing this we would be able to get exact names of the stars. Now we will be able to narrow our search to some hundreds of ly.

There we will do the trick again, only this time we will look for less bright stars like Sirius or Vega. After this we will have to check only several stars to get to the Sun.

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Going home can be easy, or it can be very hard.

  1. Very easy. Spacefaring aliens should have not only comprehensive stellar catalogs, they should have space equivalent of "Google Maps". If Average Joe knows the name of the Sun in alien language - problem is solved in one step. If he doesn't know the name, he can search for specific type of star with specific planetary system. Planetary layout supposed to be as good as stellar fingerprints - all exoplanetary systems known so far are different, and none is like our solar system.
  2. Easy. The database does not contain planetary data, but it does contain star data. Look for Alpha Centauri-type ternary system, and look for G2 class neighbor. There must be not too many to choose from.
  3. Hard. There is no database, and your traveler must make his own observations. Depending on the instruments he has it may take some time, or make the whole task impossible. It would also be very important what specific knowledge this amateur astronomer has. If he knows the general distance of the Sun from galactic center and relative position of it with respect to outside markers like Andromeda galaxy or Magellanic clouds, the search can be greatly narrowed. If not, he has to locate bright stars that would match Sun's neighborhood, like Canopus, Betelgeuse and Deneb. It is also worth noting that Sun's region may not be directly observable from his current location within the galaxy.
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Joe is lost forever, unless…

Let us assume for a moment that the aliens have transported Joe to their home world and by coincidence it is only 200 Light Years away from Sol. Within a 200 Light Year cubic volume near Earth, is approximately 32000 stars. Joe is not going to know that any given binary star might possibly be Alpha Centauri because it is 4.2 LY away from a G2V star, simply because the database available to him will not contain understandable stellar classifications, nor will it contain understandable distances. Joe may recognise that he is somewhere in the correct place near the end of the Orion Spur. Now if the alien home world is further away, let us assume that Joe can find his way back to the Orion Spur, he is still going to be hopelessly lost at that point.

The Pioneer/Voyager Maps

There is one possible way for Joe to find his way home, and that is by triangulation of the signals from Pulsars, as shown on the Pioneer Plaques, but again, that poses its own unique problems.

enter image description here https://en.wikipedia.org/wiki/Pioneer_plaque

Maps on how to find the Earth were attached to the Voyager and Pioneer probes. Does Joe have a photographic memory, and has memorised the map? Or when Joe was abducted he was carrying a book containing an image of the plaque? Not only are the periods of each pulsar encoded as binary, but the approximate distances to each pulsar are drawn on the maps. Now, the pulsar periods are not only in binary, but the time intervals are specified on the Plagues in terms of hydrogen, so Joe could use the Ships computer to translate this into the Aliens time intervals.

http://www.johnstonsarchive.net/astro/pulsarmap.html

Joe could pull up the list of galactic pulsars and triangulate to find the approximate position of the Sol system, and this will give him a position within tens of light years. Further triangulation can be made by looking up the nearby Supergiants and identifying Betelgeuse.

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I would bet that if aliens are travelling the stars, they probably aren't doing it without computers aiding in the navigation. Maybe with his amateur astronomy he can try to travel home by figuring out what the aliens call his planet. If he can't do that, maybe he can use his skills to narrow the nav computer's search. Maybe he can travel to a lot of systems with the right type of star, then explore to see if the planets are what he expects. He could also try to fly until he finds familiar constellations, then get help from the nav computer to try and "Get back" to the exact celestial patterns seen from earth (or at least close enough). I'm imagining him drawing Orion's Belt on a tablet, then asking the computer to find a similar pattern in the sky. Maybe the computer finds a few possibilities (the constellation would look different depending on where he was in the galaxy) and he has to fly certain directions to line things up correctly. Next he doodles the Big Dipper and tries to find another match. Maybe that's not very realistic, but with enough narrativium he could try it.

Also, maybe there are more than one type of alien he could meet or get help from.

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    $\begingroup$ Constellations when viewed from some other location in the galaxy (even fairly close to where we are) would at least look quite different. They might not be recognizable. $\endgroup$
    – user
    Sep 12, 2017 at 9:04
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    $\begingroup$ My cat has a chip that a computer knows is linked to my house. If you have a variety of weird alien slaves it probably makes sense to have some basic medical information embedded in them, and that might include natural habitat. $\endgroup$
    – user25818
    Sep 12, 2017 at 14:33
  • $\begingroup$ @MichaelKjörling I edited my answer to clarify that. They most certainly would look different, but a spaceship's computer or AI would certainly be be capable of finding best candidates, maybe telling the traveller "hey, I didn't quite find a perfect match, but of all the constellations you drew for me, I found a few within reasonable error." The computer then shows a near perfect big dipper and a less than perfect match of Scorpio on the display. "Hmm" the traveler thinks, "That's not quite right. Computer, where would we have to navigate to such that this star was a little to the right?" $\endgroup$
    – ryanrr
    Sep 13, 2017 at 0:14
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If he is an amateur astronomer then he'll probably know at least some of the stellar properties of solar systems near to us. Assuming he has access to an extensive alien stellar library and can match their data to what he is familiar with, he might be able to screen out the billions of G type stars that aren't our Sun. Alpha Centari is a binary (really a trinary solar system with binary suns and a distant red dwarf), Sirius A and B is a binary system, the flare star Ross 154, etc may be enough to narrow down potential Earth systems to something he could reasonably check within his (dogs) lifetime. Even more so if they also catalogue planets/moons. Of course the age of the library will have to be taken into account, proximity to other stars is pretty variable over millions of years. Once he is very close, say 100 light years or so, then he may be able to pick up radio emissions, but realistically those signals are far too weak to receive more than a few lightyears away so that won't really help unless the aliens have REALY good detection technology.

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The big problem with using the proposed images of the galaxy to navigate is when you're in space, you're essentially underwater in terms of movement (but with no bottom and no surface). It's nowhere near as easy as just following a linear path to get somewhere, and you have no idea which direction you're facing and which direction the galaxy is currently facing - direction doesn't even mean anything.

ryanrr's suggestion of an on-ship computer is sound. It's unlikely that everyone in this society is some kind of genius, our astronauts couldn't build the spacecraft they rode in on or get themselves to the moon without ground control crunching the numbers, and it's unlikely that these alien astronauts/interstellar kidnappers could do so either.

Assuming ship's computer was made to not recognize authorized pilots, and was developed with simplicity in mind for these burly, kidnapper types, Joe should be able to tell it to search for star systems with planets - if this race thinks it's cute to take slave labor from wherever in the galaxy, they've undoubtedly done a great job cataloging every star system they've discovered, possibly with a list of inhabited planets (if any), so they can go back and grab more free workers when the last set they abducted keel over. These undoubtedly come with a relative set of coordinates (which update over time in accordance with galactic movement), for quick and easy navigation.

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The Hansel Maneuver.

Hansel and Gretel and trail of pebbles

Hansel knew he would be lost in the deep forest. So he left a trail of pebbles with which he and his sister could find his way home. As he is abducted, your hero should realize the same thing that Hansel did, and surreptitiously leave a trail behind him as he travels.

Then he has only to follow the trail to find his way home.

The problem: space is big. What to leave as a trail?

I was initially thinking he could leave these.

LED pig

These things will blink a long time, work frozen in ice and do not care about vacuum. But even though they blink in different colors I suspect they would be hard to see at cosmic distances. Not impossible, if there was not much else around and you were an artificial intelligence with a telescope and image analysis.

Would some sort of radio emitter be better? A periodic chirp. One could search for the next from the vantagepoint of the last using a big dish to establish direction. Maybe that only seems better to me because we are used to seeking visible light EMR with our eyes, but seeking other parts of the EMR spectrum with machine aid.

I submit this idea because it is different from what answers are here already (which add up to pretty dim prospects for our hero, it seems to me) and plausible given sweet space MacGyver skills - not because it is a thing sure to work.

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So, I mean, his captors know where his planet is / was, yes?

If Joe is somehow using their ships, he would have the ability (in theory, and perhaps not the access) to read their star charts.

If he has their star charts but doesn't know exactly which star on the chart is home, he could use his own knowledge of the stars near Sol to narrow down his search. "Hey, this one has a binary system about 4 LY away, and is 800 LY from this one which I think might be Rigel..."

And narrow down from there.

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Milky Way is rather simple galaxy. You just locate the bar (get it, bar, in the Milky Way). Then by galactic longitude the Orion spur and at the end is our sun. Then just go where our solar system is and voila. The place of our sun in galaxy shouldn't be a secret to amateur astronomer.

Galactic Longitude

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    $\begingroup$ This may be correct (to within narrative error), but how would our intrepid hero go about doing that? $\endgroup$
    – user
    Sep 12, 2017 at 9:03
  • $\begingroup$ The problem as I see it is the process of navigating through the milky way $\endgroup$
    – Lee Leon
    Sep 12, 2017 at 10:16
  • $\begingroup$ @LeeLeon That's the narrative fuel? "The ship swiftly avoided obstacles gaining speed from gravity fields" Or something like that. $\endgroup$
    – SZCZERZO KŁY
    Sep 12, 2017 at 12:41
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    $\begingroup$ @SZCZERZOKŁY - what I meant was, if dropped anywhere within the milky way, I think it would be very very difficult to work out where that was, so the chances of working out where our solar system was, relatively, would be almost impossible. It's not as if the milky way is particularly flat, although it might be diagrammatically shown that way. $\endgroup$
    – Lee Leon
    Sep 12, 2017 at 13:57
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    $\begingroup$ @SZCZERZOKŁY - well, if I travelled in the right direction, I expect I would be able to read the labels - how far away do you think that would be from the hub? $\endgroup$
    – Lee Leon
    Sep 12, 2017 at 16:04

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