Expert: Courtney Seligman - 7/15/2008

Question
what are the errors in star parallax measurement?      thanks

Answer
(Please forgive the lateness of this answer. I volunteered on August 5, and noticed that no one had answered your question, despite its age.)

The error in the actual measurements is due to the fact that stars' positions can only be measured to some fraction of a second of arc, typically in the neighborhood of 1/20" for a single Earth-based observation, 1/100" for observations from space, and 1/500" for an average of many positional measurements from space. With new satellites, due to be launched in 2012, individual measurements may approach an accuracy of 1/1000".

How important these errors are depends upon the actual parallax of a star. If a star is very close, so that its parallax is several tenths of a second of arc, a 1/100" error will produce an uncertainty in its distance of only a percent or two; while if it is a hundred parsecs (about 326 light years) away, its parallax is only 1/100" of arc, and the uncertainty in its distance would be infinite (it could be two or three times closer than the best estimate of its distance, or infinitely far away).

Let me know if you need a more or less detailed answer than the above.