# Astronomy question - do stars retain relative position each year viewed from earth? **URL:** \ **Category:** Factual Questions\ **Created:** [July 20, 2007, 1:08pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533 "2007-07-20T13:08:15Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Wallenstein](https://avatars.discourse-cdn.com/v4/letter/w/b5a626/32.png) [@Wallenstein](https://boards.straightdope.com/u/Wallenstein)\ **Post date:** [July 20, 2007, 1:08pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/1 "2007-07-20T13:08:15Z")
Say I were to look due north at midnight on 1 Jan 2008 from a given location, are the stars I would see in the same place as they were on 1 Jan 1998, or 1 Jan 1808? The reason I ask comes from this site: [http://www.grahamphillips.net/Ark/Ark\_10.htm](http://www.grahamphillips.net/Ark/Ark_10.htm) and specifically [this picture](http://www.grahamphillips.net/Ark/epiphany_window.jpg). The author claims that by viewing night sky at midnight on 6 Jan from a particular hill in South Warwickshire, you can deduce the resting place of the Ark of the Covenant. Now this is only 20 mins from my house, so it’s all quite exciting. BUT… the whole premis seems to rely on the fact that the stars would be in the same position at that specific time as they were 100 yrs ago (or whenever the window was created). By drawing a line through two stars in The Plough (which are linked to the Ark legend) it hits a point on the horizon - [like this](http://www.grahamphillips.net/Ark/Ark_11_files/star_line.jpg) - and there lies the Ark (or so it goes). If the stars don’t stay constant, that line could be anywhere though, hence my question. 🙂 ---
**Author:** ![Alive\_At\_Both\_Ends](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@Alive\_At\_Both\_Ends](https://boards.straightdope.com/u/Alive_At_Both_Ends)\ **Post date:** [July 20, 2007, 1:30pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/2 "2007-07-20T13:30:42Z")
The stars stay in roughly the same configuration from one year to the next, but over a period of centuries they do not. [Precession](http://en.wikipedia.org/wiki/Precession_%28astronomy%29) causes the direction of the Earth’s axis to change over a long period which means that the stars do not appear in the same position on 1 Jan 2008 as they did on 1 Jan, say 1608. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [July 20, 2007, 1:31pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/3 "2007-07-20T13:31:02Z")
Strictly speaking, no, it’s not _exactly_ the same. The stars have what’s called [proper motion](http://en.wikipedia.org/wiki/Proper_motion), and their absolute position on the sky does change with time. However, this change is very, very slow; the star with the highest proper motion, Barnard’s Star, would take about 360 years to move one degree on the sky. (And Barnard’s Star isn’t even visible to the naked eye.) I also managed to find a [movie of proper motions in the Big Dipper](http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Movies/proper.html) (what we call that collection of stars on this side of the pond.) Notice that every frame in this movie is a thousand years, and that the shape of the Big Dipper hasn’t changed significantly over human history. However, if you’re talking about extrapolating lines down to the horizon, then these small changes might indeed be enough to throw you off. ---
**Author:** ![Baron\_Greenback](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/baron_greenback/32/48_2.png) [@Baron\_Greenback](https://boards.straightdope.com/u/Baron_Greenback)\ **Post date:** [July 20, 2007, 1:33pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/4 "2007-07-20T13:33:58Z")
[Here’s a nice academic page](http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit1/motions.html) explaining the motion of the stars. ---
**Author:** ![Malodorous](https://avatars.discourse-cdn.com/v4/letter/m/e47774/32.png) [@Malodorous](https://boards.straightdope.com/u/Malodorous)\ **Post date:** [July 20, 2007, 1:37pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/5 "2007-07-20T13:37:17Z")
[QUOTE=Alive At Both Ends] The stars stay in roughly the same configuration from one year to the next, but over a period of centuries they do not. [Precession](http://en.wikipedia.org/wiki/Precession_%28astronomy%29) causes the direction of the Earth’s axis to change over a long period which means that the stars do not appear in the same position on 1 Jan 2008 as they did on 1 Jan, say 1608. [/QUOTE] Precession doesn’t change the _relative_ position of the stars though, just the position of the “celestial sphere” relative to the Earth. Good luck on your Ark hunt, watch out for Nazis ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [July 20, 2007, 1:39pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/6 "2007-07-20T13:39:37Z")
[QUOTE=MikeS] I also managed to find a [movie of proper motions in the Big Dipper](http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Movies/proper.html) [/QUOTE] Cool! Now I know why people from 98,000 years in the future call it the ‘Meat Cleaver’. ---
**Author:** ![Alive\_At\_Both\_Ends](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@Alive\_At\_Both\_Ends](https://boards.straightdope.com/u/Alive_At_Both_Ends)\ **Post date:** [July 20, 2007, 1:46pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/7 "2007-07-20T13:46:26Z")
[QUOTE=Malodorous] Precession doesn’t change the _relative_ position of the stars though, just the position of the “celestial sphere” relative to the Earth. [/QUOTE] I know that, but that still means that those two stars in the Plough won’t point to the same point on the horizon over time. ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [July 20, 2007, 1:48pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/8 "2007-07-20T13:48:25Z")
[QUOTE=Malodorous] Precession doesn’t change the _relative_ position of the stars though, just the position of the “celestial sphere” relative to the Earth. Good luck on your Ark hunt, watch out for Nazis [/QUOTE] But they would change what the OP is asking about though—the alignment of the stars with ground features. Right? ---
**Author:** ![Malodorous](https://avatars.discourse-cdn.com/v4/letter/m/e47774/32.png) [@Malodorous](https://boards.straightdope.com/u/Malodorous)\ **Post date:** [July 20, 2007, 2:35pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/9 "2007-07-20T14:35:38Z")
[QUOTE=toadspittle] But they would change what the OP is asking about though—the alignment of the stars with ground features. Right? [/QUOTE] Quite right, I just glanced at the OP’s links and so misunderstood. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [July 20, 2007, 2:55pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/10 "2007-07-20T14:55:07Z")
Wouldn’t our orbit around galactic center also have an effect? Also slow (a bit over 100 million years to go half way around) so even on an all of human history timescale we have not moved all that much (relatively speaking) but still… ---
**Author:** ![Freddy\_the\_Pig](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Freddy\_the\_Pig](https://boards.straightdope.com/u/Freddy_the_Pig)\ **Post date:** [July 20, 2007, 3:10pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/11 "2007-07-20T15:10:44Z")
[QUOTE=Whack-a-Mole] Wouldn’t our orbit around galactic center also have an effect? Also slow (a bit over 100 million years to go half way around) so even on an all of human history timescale we have not moved all that much (relatively speaking) but still… [/QUOTE] That’s part of “proper motion”, and on the time scales that we’re talking about here, not a terribly important part. All stars are in orbit around the galactic center, but with irregular movement superimposed upon those orbits, and that irregular movement makes up most of what we see as proper motion. (If all the stars were in perfectly regular orbits, then we’d see very slow and very regular movement more like what we see on a smaller and faster scale with the planets.) ---
**Author:** ![Wallenstein](https://avatars.discourse-cdn.com/v4/letter/w/b5a626/32.png) [@Wallenstein](https://boards.straightdope.com/u/Wallenstein)\ **Post date:** [July 20, 2007, 8:03pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/12 "2007-07-20T20:03:43Z")
Thanks all - apparently they found one of the tablets containing the [Ten Commandments](http://www.grahamphillips.net/Ark/stone_slab_large.jpg) in a ditch, but I’m hoping there’s some more left to find. 😉 Useful links - sounds like a 19th century star code will still be more-or-less valid today, so the map inference remain valid (although still waaaay over the kook-horizon). ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [July 20, 2007, 11:09pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/13 "2007-07-20T23:09:07Z")
well, I have to say, that’s a lot more convienient that carrying that pesky Staff of Ra headpiece around. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 20, 2007, 11:34pm UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/14 "2007-07-20T23:34:13Z")
On a related subject, the U.S. Department of Defense spends millions of dollars every year tracking the precise position of the North Star relative to earth. The measurement is performed each night (assuming there’s no cloud cover). I’ve been to the facility. Quite fascinating. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [July 21, 2007, 12:35am UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/15 "2007-07-21T00:35:55Z")
Good old DoD … Gotta keep a close & wary eye on that Polaris; it might shift into attack formation at any moment. 🙂 ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 21, 2007, 1:07am UTC](https://boards.straightdope.com/t/astronomy-question-do-stars-retain-relative-position-each-year-viewed-from-earth/412533/16 "2007-07-21T01:07:46Z")
And there is [Barnard’s Star.](http://www.solstation.com/stars/barnards.htm) Sometime faceciously called Barnard’s Comet.