So the question is simple. How many light years would we have to go from Earth until we would be unable to determine known constellations?

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    $\begingroup$ This question seems to have a false premise - you can't determine your position purely based on constellations (aka a 2D image of the sky) even within the close vicinity of Earth. $\endgroup$
    – asdfex
    Commented Feb 5, 2021 at 18:27
  • $\begingroup$ @asdfex point taken, edited. The point is, how far out from Earth would we get "Lost in space" $\endgroup$ Commented Feb 5, 2021 at 20:58
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    $\begingroup$ Welcome to Space Stack Exchange. I think this is an interesting question but needs some clearer language. Is your whole point actually that @asdfex 's comment only applies close to Earth and therefore one would know one was "not near Earth" if there were only 50% recognisable constellations. Also "not near Earth" is a bit step from knowing one's location. Its going to come down to you setting an arbitrary threshold of the fraction of constellations with stars close to Earth, say 10%, for one to notice that something "isn't right". $\endgroup$
    – Puffin
    Commented Feb 5, 2021 at 21:29
  • $\begingroup$ After that you have to set another arbitrary threshold for the visible magnitude, i.e. if you just looked at the faintest stars then @asdfex 's comment would apply all the time. Hence this threshold would have to be defined as, say, that you'll only bother with those visible with the naked eye. After all this, whilst the question sounds like its about exploration you are much more likely to find people handy with star catalogues who could answer all this on Astronomy SE. Anyway, lets see what happens. $\endgroup$
    – Puffin
    Commented Feb 5, 2021 at 21:30
  • $\begingroup$ I think a good approach to answering this would be incremental: you are allowed to estimate your position relative to Earth with such precision, that performing a hyperspace jump to calculated location will improve your next estimate by an order of magnitude. E.g. if you're in the Andromeda galaxy, locating Milky Way would be good enough; with Milky Way in good view you can reach the right area of the right arm of it, and so on. ...and in this case you can't, at least within our observable universe and with a good navigation computer and telescope capable of spotting the filaments. $\endgroup$
    – SF.
    Commented Feb 5, 2021 at 22:18

1 Answer 1


Well, we can determine positions of galaxies in a very large region of Universe with precision of about 1%. So if we're talking about relative accuracy (bigger error is acceptable on bigger distance from Earth), then in static Universe we probably would be able to venture billions of light-years and still know our position relatively to Earth up to 10% error margin. Finding approximate direction to Earth is even easier.

Unfortunately real Universe is moving and evolving, so probably if you travel for billion of light-years it will change too much for existing maps to be still useful for navigation. So we should restrict ourselves a bit in time. Still you can likely go for dozen millions of light-years and will still approximately know where you are.

Surprisingly navigating within our own galaxy might be more complex. We need stars for navigation with good accuracy on a galactic scale, but interstellar gas and dust clouds block large regions of our galaxy from our sight. So I'd say we need to go to probably 40 million of light years in specific direction (towards Milky Way center) to get lost. You might get lost even closer if you'll end inside of sufficiently dense gas or dust cloud that will block even IR light (but it's hard to find and maybe we still would be able to see some stars with radio astronomy even in that case).

Like before, time is also an important factor. Wait long enough and your maps will became obsolete even if you hasn't moved far away. Stars are changing their positions far faster than galaxies so even few hundreds thousands of years will present a challenge.

Of course navigation in all cases should be based on modern star maps like one that Gaia satellite produces rather than "constellations".


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