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B How do astronomers find the "parallax angle" of a star?

  1. Dec 15, 2017 #21
    Ah yes, thank you.

    Sounds like using parallax to measure the distance to binary stars might be a bit of a pain.
  2. Dec 15, 2017 #22
    Not really, there are alot of thing much more complicated in science and it depends a lot on how accurate you want it to be. The basic concept is very simple but if you want ridiculously accurate measurements (and an equally ridiculously amount of them) you get something like the GAIA spacecraft.
  3. Dec 15, 2017 #23


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    It depends on the orbit, but some binary stars are certainly more complex. You can also see this in the Gaia data release plans. Data releases for multiple star systems are behind releases for single-star systems because it takes longer to measure and analyze them.
  4. Dec 15, 2017 #24
    This is fascinating. Thank you.
  5. Dec 17, 2017 #25


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    You can use any star database to find the angular separation between two known stars and, compare two photos, taken 6months apart. The stars that are far enough away to be regarded as 'fixed' are your backdrop and you measure the change in position of your star-under-test. You need to do some measuring of distances on the photos and use the known angular separations and some 'Ratios' to tell you the angle scale of your photo. (Use several known stars to help your accuracy).
    To increase your accuracy, you may need to measure and correct for the field distortions in your lens (shift the image around and compare the distance when stars are on the edge and in the middle) and do your measurements near the axis of the lens. Of course, you need to choose stars that are separated by only a very few degrees so the error is small. (tanθ ≅ sinθ ≅ θ in radians as θ→ 0)
    To ameliorate the effect, you do it with the Earth moving one direction (right-left) in its orbit and then, later the other way (left-right). The 'correct' / better answer is the mean of the two apparent parallax values. A tedious and time consuming process but less so than when people had to sketch or use photographs. We have it relatively easy these days.
  6. Dec 17, 2017 #26

    stefan r

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    A mural instrument was the classic:

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