# Can you find your way home from far FAR away? **URL:** \ **Category:** Factual Questions\ **Created:** [December 10, 2008, 4:50pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570 "2008-12-10T16:50:02Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [December 11, 2008, 1:32pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/41 "2008-12-11T13:32:46Z")
I just want to comment that this is a highly interesting thread. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [December 11, 2008, 2:05pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/42 "2008-12-11T14:05:44Z")
I don’t think that anyone has mentioned the fact that all the stars in the Milky Way are rotating around it’s center. If you traveled very far away (and it took a very long objective time), the Galaxy wouldn’t look the same as when you left. That might complicate things quite a bit. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [December 11, 2008, 2:49pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/43 "2008-12-11T14:49:05Z")
> [@beowulff](#): > > I don’t think that anyone has mentioned the fact that all the stars in the Milky Way are rotating around it’s center. If you traveled very far away (and it took a very long objective time), the Galaxy wouldn’t look the same as when you left. That might complicate things quite a bit. Even if you travel instantaneously, it wouldn’t look the same. Remember that from Earth, we are seeing the stars where they were however many light years away they are years ago. Also remember that part of the semi-common theme is that once our hero is shot through a wormhole or becomes lost in space, they often have a hard time finding their way back. ---
**Author:** ![groman](https://avatars.discourse-cdn.com/v4/letter/g/73ab20/32.png) [@groman](https://boards.straightdope.com/u/groman)\ **Post date:** [December 11, 2008, 2:58pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/44 "2008-12-11T14:58:32Z")
It also depends on how much information the aliens have in their galactic computers. If they have our solar system mapped with any sort of detail then wouldn’t it be fairly easy to find, especially if you have a wrist watch to show them? I mean how many planets with liquid water oceans are there with a 365 day year and a 24 hour day that are the third planet from its sun in the galaxy? If the aliens have any sort of gravity simulator thing you could probably have them increase your weight from 0 to X and you can point out the range that “feels right”, which should also give them a good idea about the mass of Earth. If they have such stats in their great galactic encyclopedia, it should identify a few likely candidates. As for memorizing location information that pinpoints the star not the planet, I would imagine that if you memorize distances from Sol to nearest 10 or 20 stars with any sort of precision using some non-earth-centric distance unit that you could explain should pin-point it quite a bit given any sort of galactic map that only has stars on it. Something like a list: 4.2, 4.3, 4.3, 6.0, 7.8, 8.2, 8.6, etc. My gut feeling tells me that there’s a degree of precision for such a list that would pretty uniquely identify Sol within a certain radius. The greater the precision the greater the radius. ---
**Author:** ![Wiltshire](https://avatars.discourse-cdn.com/v4/letter/w/ea5d25/32.png) [@Wiltshire](https://boards.straightdope.com/u/Wiltshire)\ **Post date:** [December 11, 2008, 3:55pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/45 "2008-12-11T15:55:36Z")
If I recall correctly, the characters in the novel _Douglas Adams’s Starship Titanic_ found themselves in exactly this predicament. Lost, with the alien people willing to send them back, but no idea where to.The way home is determined with the help of a photograph; a nighttime exposure taken on Earth in which the local star constellations were visible. ---
**Author:** ![chromaticity](https://avatars.discourse-cdn.com/v4/letter/c/cc9497/32.png) [@chromaticity](https://boards.straightdope.com/u/chromaticity)\ **Post date:** [December 11, 2008, 4:27pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/46 "2008-12-11T16:27:21Z")
What! No Farscape references yet! ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [December 11, 2008, 5:27pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/47 "2008-12-11T17:27:20Z")
> [@Sigmagirl](#): > > You should. You’ve driven past it nine times. :: bored voice from the back seat :: Are we there yet…? Great thread, BTW. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [December 11, 2008, 6:02pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/48 "2008-12-11T18:02:38Z")
> [@groman](#): > > It also depends on how much information the aliens have in their galactic computers. If they have our solar system mapped with any sort of detail then wouldn’t it be fairly easy to find, especially if you have a wrist watch to show them? I mean how many planets with liquid water oceans are there with a 365 day year and a 24 hour day that are the third planet from its sun in the galaxy? If the aliens have any sort of gravity simulator thing you could probably have them increase your weight from 0 to X and you can point out the range that “feels right”, which should also give them a good idea about the mass of Earth. If they have such stats in their great galactic encyclopedia, it should identify a few likely candidates. If they have our solar system mapped sufficiently to know what earth’s gravity is, I kind of think they might even recognize humans. ---
**Author:** ![aerodave](https://avatars.discourse-cdn.com/v4/letter/a/f08c70/32.png) [@aerodave](https://boards.straightdope.com/u/aerodave)\ **Post date:** [December 11, 2008, 6:04pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/49 "2008-12-11T18:04:09Z")
> [@groman](#): > > As for memorizing location information that pinpoints the star not the planet, I would imagine that if you memorize distances from Sol to nearest 10 or 20 stars with any sort of precision using some non-earth-centric distance unit that you could explain should pin-point it quite a bit given any sort of galactic map that only has stars on it. > > Something like a list: 4.2, 4.3, 4.3, 6.0, 7.8, 8.2, 8.6, etc. > > My gut feeling tells me that there’s a degree of precision for such a list that would pretty uniquely identify Sol within a certain radius. The greater the precision the greater the radius. I wonder if there’s something to this. If you had a catalog of the position of every star int he galaxy, it should be possible (but beyond my means) to mathematically determine how far down the list you have to memorize to uniquely determine which star is the sun. If there are 300 billion stars in the Milky Way, some number will be 4.2 ly to the nearest star (within some margin). Maybe there are still billions. Only some of those will be 4.3 ly to the binary star system that makes the second and third closest stars. Maybe millions. And even fewer will be 6.0 ly from the fourth nearest star…and so on. So assuming a random distribution of 300 million stars in the galaxy, and an error of ±0.1 ly in the measurements, how far down the list should you need to go to whittle it down to one? Here’s my math based on very rough assumptions that you’re free to debate at length: I’m sure the distribution of distances between all the stars in the galaxy and their nearest neighbor is some Gaussian function that goes from 0 to a big number, but I don’t know what the mean or spread would be, and don’t care to do napkin math with weird functions. So let’s say that the possible distances of stars to their nearest neighbors must be between 2 and 9 light years (a range of 7), and is evenly distributed in that range. So any given distance you pick (±0.1 ly) will comprise 0.2/7 or 1/35 of that range. So knowing a star’s nearest neighbor distance has reduced the list from 300 billion to 1/35 of that (or 85 billion). Now repeat this for the next nearest. Maybe you assume that the range is now 3 to 10 light years, or whatever. But for now I’m keeping my assumption that leads to each known distance cutting the list by a factor of 35. If you keep repeating this, you end up reducing the list to less than 1 (uniquely determining the right star) with the 8th distance on the list. You may need more, or you may need less. But it suspect the answer is in that ballpark. 1 is too few, and 100 is too many. So if you leave Earth having memorized the distances to the closest 10 stars, you’ll probably have enough information. 15 should be really safe. Now of course, having any other information to narrow it down would help significantly. If you remember that the Sun is between 25,000 and 30,000 light years from the galactic center, then you should be able to narrow down the choices by a huge margin from the get-go. If you know the size or spectral class of the sun (and can meaningfully communicate this with the aliens), you could probably pinpoint it very quickly with only the distances of a few neighbors. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [December 11, 2008, 7:32pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/50 "2008-12-11T19:32:59Z")
> [@Chronos](#): > > .. And directions you can communicate just by pointing… If the aliens are anything like dogs or many other higher animals, they’ll just look at your finger. ---
**Author:** ![MrFloppy](https://avatars.discourse-cdn.com/v4/letter/m/43a26b/32.png) [@MrFloppy](https://boards.straightdope.com/u/MrFloppy)\ **Post date:** [December 11, 2008, 9:06pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/51 "2008-12-11T21:06:44Z")
Hopefully, you would have a copy of [Celestia](http://www.shatters.net/celestia/) on your laptop. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 11, 2008, 10:08pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/52 "2008-12-11T22:08:11Z")
> [@](#): > > If the aliens are anything like dogs or many other higher animals, they’ll just look at your finger. Dogs and other social animals generally do understand pointing (except for the really dumb dogs, but they generally can’t operate warp-drive ships). Heck, even bees have something analogous to pointing that they understand. It’s cats that’ll just look at your finger. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [December 11, 2008, 10:15pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/53 "2008-12-11T22:15:13Z")
I think not. But I will grant that some life form that has captured someone from here is likely to be able to interpret that gesture. ---
**Author:** ![gonzomax](https://avatars.discourse-cdn.com/v4/letter/g/e8c25b/32.png) [@gonzomax](https://boards.straightdope.com/u/gonzomax)\ **Post date:** [December 11, 2008, 10:45pm UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/54 "2008-12-11T22:45:16Z")
[http://us.st12.yimg.com/us.st.yimg.com/I/spaceimages\_2030\_11422680](http://us.st12.yimg.com/us.st.yimg.com/I/spaceimages_2030_11422680) The ball of land and water disappears quickly as you travel away. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [December 12, 2008, 1:33am UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/55 "2008-12-12T01:33:18Z")
> [@gonzomax](#): > > [http://us.st12.yimg.com/us.st.yimg.com/I/spaceimages\_2030\_11422680](http://us.st12.yimg.com/us.st.yimg.com/I/spaceimages_2030_11422680) The ball of land and water disappears quickly as you travel away. Is that just supposed to be a static image? From how far away is it, or is it meant to be? ---
**Author:** ![CutterJohn](https://avatars.discourse-cdn.com/v4/letter/c/91b2a8/32.png) [@CutterJohn](https://boards.straightdope.com/u/CutterJohn)\ **Post date:** [December 12, 2008, 1:40am UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/56 "2008-12-12T01:40:32Z")
once you get within 50 or 100 ly, shouldn’t you be able to pick up(with suitably sensitive gear) radio transmissions from earth? This may help once you find it once you get close enough. Other than that, I imagine an astronomer or astronomy buff might know enough to get back home, but most people… Not really. All I really know is that the solar system has 8 major planets and one major asteroid belt, and that there is a solar system ~4 ly away, and a horribly generalized concept of where earth is on one of the arms(though I don’t know which). Not a lot of information to work with, unfortunately, so I don’t imagine i would be seeing home again. Not that I’d really want to, however. ---
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [December 12, 2008, 2:25am UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/57 "2008-12-12T02:25:48Z")
Wouldn’t it make sense to make units everyone could understand? If, before we get abducted, just make a point to say 1GUD (Galactic Unit of Distance) is, say, the diameter of the Galaxy, and 1 GUT (… of Time) is, say, one revolution of the galaxy (it is revolving, right?) then it wouldn’t be a stretch to idiomatically remember that the Earth is (made up number) 1/14th of a GUD in from the edge and figure out other absolute positions relating to the center to just work out where the Earth is any time you see a galactic map. Or even better, since it gives you an obvious unit of time everyone will know simply explain 1 year is (made up numbers) 1/9826541 GUT, 1 meter is 1/2847384735 GUD and let them do the conversion of the Speed of Light in m/s to their own units and then proceed to do the tricky stuff with nebulae and whatnot mentioned earlier in the thread. I’ll admit the one flaw is it won’t help you extragalactically, but oh well. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [December 12, 2008, 3:00am UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/58 "2008-12-12T03:00:18Z")
The galaxy is composed of individual stars which revolve around the center with different “years” just as the planets of the solar system do so there is no simple galactic year. The galactic diameter is not quite so nebulously (pun intended) defined, but it’s not well defined either since the stars sort of peter out. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [December 12, 2008, 3:42am UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/59 "2008-12-12T03:42:11Z")
> [@OldGuy](#): > > True three spheres will intersect in two points so a fourth would help. Also there would be more intersections since each year could correspond to any of the three supernovae. Even though some of the intersections might be far outside the galaxy, I suspect pinpointing one would help a great deal. You’d be unlucky if the other intersections had a star like ours at them ---
**Author:** ![dotchan](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@dotchan](https://boards.straightdope.com/u/dotchan)\ **Post date:** [December 12, 2008, 4:32am UTC](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570/60 "2008-12-12T04:32:28Z")
If I did end up stranded on some distant galaxy, I think I’d be more likely to settle down unless the Sufficiently Advanced Aliens had faster-than-light space travel, because time-dilation would mean that I wouldn’t make it back (if I could at all) until centuries after everybody I cared about died. [Previous page](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570.md?page=2) [Next page](https://boards.straightdope.com/t/can-you-find-your-way-home-from-far-far-away/476570.md?page=4)