I’m trying to understand how to measure the distance to nearby stars using the parallax method.
My question is: how do you get the value of the p angle?
Astronomy Stack Exchange is a question and answer site for astronomers and astrophysicists. It only takes a minute to sign up.Sign up to join this community
In actual fact its a bit more complicated, because
The combination of these errors is what limits the use of parallax method for distance measurement to about 150 parsecs. For observations of more distant stars the errors overwhelm the observed motion and alternate measurement method are needed.
You might consider reading through https://en.wikipedia.org/wiki/Stellar_parallax , it explains a lot.
You measure it on the photographs.
If you take multiple images of the same star over the year you will find that it moves in a loop (compared to the very distant background stars) You measure the size of the loop. A larger loop is a larger angle. Because the angles are small, the size of the loop is in direct proportion to the angle. If you know the scale of the photograph, you can find the angle directly.
In practice, there are difficulties: The star is moving, so rather than a closed loop, it will trace a helical path in the sky. Your images may be distorted by the atmosphere, making it hard to exactly locate the star, and the star may not be visible for several months of the year when it is behind the sun (from our perspective). The difficulties can be overcome by taking a series of images over a longer period of time.