[Learning is Fun] Parallax
I added star descriptions on the above flickr photo I took on the 20th. Just click on the picture above and then mouse over the photo to the notes (above the stars)
I think I ought to bring up something called parallax. According to wikipedia, parallax is the only direct method by which distances to objects beyond the Solar System can be measured. The Hipparcos satellite has used the technique for over 100,000 nearby stars.
Precise parallax measurements of distance usually have an associated error. Thus a parallax may be described as some angle ± some angle-error. However this "± angle-error" does not translate directly into a ± error for the range, except for relatively small errors. The reason for this is that an error toward a smaller angle results in a greater error in distance than an error toward a larger angle.
However, an approximation of the distance error can be computed by means of the following:
where d is the distance and p is the parallax. The approximation is far more accurate for parallax errors that are small relative to the parallax than for relatively large errors.