I read a post here on PF about angular diameter, https://www.physicsforums.com/showthread.php?t=91704 I *THINK* I understand the math, my question is the actual measurement of Jupiter. Is it done at zero magnification (how?!) or 100x or ??x And with what piece of equipment?
Actual measurements can be done with telescopes, but the magnification does not matter, you just have to take it into account in the calculation. Space probes there can measure the diameter (and shape) more accurately.
What I believe that mfb is trying to say is that angular diameter, unless otherwise stated, is taken to be the angle formed between two lines whose meeting point is at the observer and whose ends fall on opposite sides of the object being measured.