If galaxies are moving Earthwards, how close to us are they really?

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Offline Fozzie

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The Andromeda Galaxy is approx 2.5 million light-years away and is moving towards us at 300km/sec. If this is the case, and we are seeing it as it was 2.5 million years ago, surely it will have moved considerably nearer to us since then, so although we cannot see it, the actual distance will be a lot less, or does the given distance take this into account? (I haven't done the maths)

This theory can also be applied to those galaxies at the edge of the universe which are moving away from us making them actually further away than the distance we observe today.  [???]
« Last Edit: 06/11/2009 17:15:09 by daveshorts »

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Offline Nizzle

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It will be less, but "alot" on astronomical scale, perhaps not
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Offline sadarian

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I believe it's still going to be around 3 billion years before the two collide. So even though 300km/sec is considerably fast, it looks like its not really fast enough to start ticking away light years from the calculation just yet. 

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Offline LeeE

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We can only actually measure the distance as it was when the light left.  However, although Andromeda is moving towards us at about 300 km/s, this only about 1/1000th of the speed of light, so it's not really significantly nearer to us than it appears to be.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Fozzie

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We can only actually measure the distance as it was when the light left.  However, although Andromeda is moving towards us at about 300 km/s, this only about 1/1000th of the speed of light, so it's not really significantly nearer to us than it appears to be.

Ah! that clears it up nicely. Thank you very much.