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With the launch of the GAIA mission some years ago, a new precedent was set in mankind's ability to map our universe. However, how accurate are the distances created by this? From ESA's website, I found:

In the final Gaia catalogue, expected in the early 2020s, brighter objects (3-13 magnitude) will have positions measured to a precision of 5 microarcseconds, parallaxes to 6.7 microarcseconds, and proper motions to 3.5 microarcseconds per year

If we take the value 6.7, and put that into the equation: d=1/p, we get d=1/0.0000067=150,000 parsecs. This is immensely accurate given that most sources tell me that the most accurate is around 1000 parsecs (accurate to 0.001 arcseconds). Are my calculations correct, or did I use a wrong value somewhere?

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  • $\begingroup$ Are you asking if ESA made a mistake? $\endgroup$
    – my2cts
    Jun 9 '18 at 18:21
  • $\begingroup$ I'm asking if I'm calculating it correctly $\endgroup$
    – Eames
    Jun 9 '18 at 18:41
  • $\begingroup$ O, I see. I will change my answer accordingly. $\endgroup$
    – my2cts
    Jun 9 '18 at 20:05
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The number is the accuracy. So for a star at 15.000 parsec that is a parallax of 67 micro arcsec this would mean a 10% accuracy of that distance.

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  • $\begingroup$ Thank you for your answer. However, I don't understand where 10% accuracy comes from? Would a star at 1,500 parsecs have 1% accuracy then? $\endgroup$
    – Eames
    Jun 9 '18 at 20:46
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    $\begingroup$ Correct. 1500 parsec corresponds to 670 micro arcsec and the precision of 6.7 micro arcsec gives 1 % precision of the distance, so $\pm$ 15 parsec. $\endgroup$
    – my2cts
    Jun 9 '18 at 21:35

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