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Cosmological distances

21 Feb 2009, 11:02 UTC
Cosmological distances
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From a little tidbit by an interested informer, I got to learn about someone wondering if the measured distances of stars and galaxies are really applicable when it takes so long for their light to reach us, that their actual distances now could be completely different. It is actually a bit mind-bending to think [...]From a little tidbit by an interested informer, I got to learn about someone wondering if the measured distances of stars and galaxies are really applicable when it takes so long for their light to reach us, that their actual distances now could be completely different. It is actually a bit mind-bending to think about all the issues, which happen to be the sort of thing I love to think and explain, except my explanation was getting rather long for a comment.

For relatively close objects (the Andromeda galaxy would count as relatively close in this context!), the notion of a distance is pretty clearcut. The observed distances should pretty much be the distances now, unless we’re missing something drastic that has happened in the meantime. So for Alpha Centauri, whose light took about four years to reach us, it should still be about four light-years ...

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