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Thread: How do we know how far away objects are in space

  1. #1 How do we know how far away objects are in space 
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    The title is fairly straightforward but let me show an example

    The galaxy, SXDF-NB1006-2, which lies 12.91 billion light-years from Earth was spotted by the Subaru and Keck Telescopes in Hawaii.
    However, my question is that how do we know how far that object is away from us? From my understanding, we would have to wait 12.91 billion light years for the light to hit our telescope before we can find even faintest trace of it.

    It may be a fairly simple question to answer, however I've been curious for a long time.


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    Forum Professor river_rat's Avatar
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    There are a multitude of methods to determine something's distance from us. For closer objects (like the moon) we can now use laser range finding or radio range finding for most other objects in the solar system. For things further out we can use parallax, take two measurements of the relative position in the sky of the object in question at different times of the year and then its "simple" trig. However, this method is only good to a couple of thousand light years at most (maybe a couple of hundred, this is all a bit rusty). We then can use relative brightness of the stars to measure their distances from us and this is pretty good for stars in the milky way. For greater distances we use the standard candle method, which is a generalization of the relative brightness idea. We start off using Cepheid Variable stars where we know the relationship between luminosity period and absolute brightness and then slowly graduate to quasars etc. For things very far away we can use red-shift as well.


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    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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    Brassica oleracea Strange's Avatar
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    ei incumbit probatio qui dicit, non qui negat
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