All stars are revolving around the center of galaxy. And so I wonder how long it takes before we can see any noticeable change in the shape of any constellation? What are the factors one will use to find this besides the speed of revolution of the concerned stars? Let us say a noticeable change corresponds to about 30 arc minutes.
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All stars have some motion relative to us called the proper motion, though only nearby stars or fast moving stars have a big enough proper motion for it to be easily measured. Lots of stars move at several arc seconds per year so 30 arc seconds would take only a few years (is 30 arc seconds really "noticable"? - I doubt I'd notice it!).
When a change to a constellation becomes noticable is I'd guess a matter of judgement. This site shows changes in the better known constellations after 50,000 years. I'm sure Googling will find many similar sites.
joshphysics
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John Rennie
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Thank you for "Proper motion". And I have changed noticeable to 30 arc minutes, which will be noticeable by human eyes. Earlier I meant noticeable by a telescope. But i think for the whole shape to appear changed, we need shifts in order of few degrees. – Nix Jul 10 '13 at 07:14