I'm writing a science fiction short story which involves a group of people being in suspended animation for a very long period of time, on the order of thousands of years.

My question is, would an astronomer on waking be able to determine that a significant period of time has passed purely by making observations in the night sky? How accurate would they be?

For the purposes of the story, I'm more interested in what an astronomer could observe unaided or with a primitive telescope of the sort Galileo might have had early in his career (around 3X magnification).


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    $\begingroup$ There are a lot of methods in which someone might try to accomplish this. What method they employ would depend highly upon what they knew before going into their suspended animation. Presumably, as you mention that they are an astronomer, they would have been well versed in astronomy before going to sleep? Would they have a modern understanding of Astronomy but rudimentary tools? Or rather primitive understanding? $\endgroup$ Commented Mar 31, 2015 at 2:48
  • $\begingroup$ @Mitch Please assume that they are a modern astronomer working at professional level before going into suspension. Afterwards, they would only have access to primitive technology. $\endgroup$ Commented Mar 31, 2015 at 3:02
  • $\begingroup$ Okay, great. Also would they have access to modern data (physical or digital), or be working with only what they might reasonably remember? Ahh, one last thing. Are we to assume that they are on Earth? $\endgroup$ Commented Mar 31, 2015 at 3:03
  • $\begingroup$ Yes, they're on Earth. Around 10,000 years has passed (but they don't know it). They only have what they remember and what they had on their person at the time of the event (i.e. clothes, keys, wallet, maybe a phone, that kind of stuff). All civilisation has decayed from lack of maintenance in the meantime, so buildings, roads, vehicles, industrial facilities, and of course, observatories, libraries, etc, are all buried rubble and rust. Civilisation is restarting, so primitive industry only is available, mostly rebuilt from memory. $\endgroup$ Commented Mar 31, 2015 at 3:11
  • $\begingroup$ Yes because of en.wikipedia.org/wiki/Proper_motion -- positions of the stars change with respect to each other over time. Assuming you knew these proper motions before going into suspended animation (which professional astronomers would know, at least for some of the faster stars [on Earth, Barnard's Star for example]), you could easily calculate how much time had passed. $\endgroup$
    – user21
    Commented Mar 31, 2015 at 17:06

1 Answer 1


In the night sky in 10,000 years, two things will have changed in relation to the stars. The first, the rotational axis of the Earth will have changed, shifting the celestial sphere. The second, the stars themselves will have moved a bit relative to each other due to proper motion. So, the night sky will be quite different in 10,000 years, but still recognizable, particularly the constellations which will have changed somewhat but will still be identifiable. I would posit that as long as the person or persons were at least casual star gazers or astronomy enthusiasts (not even necessarily professionals) they could estimate how much time has passed in the course of their slumber, I'd say with a margin of error of about +/-2000 years. Should they be trained astronomers that margin of error should fall.


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