Hi community, I get the concept of trig parallax and the apparent shift of nearby stars when viewed against a distant background, by viewing the star in say summer and then winter and it appears to move against the much further away distant background. I get what the angle p represents from the diagram above. To find the angle p, would the astronomer (in June say) star the telescope point along a line parallel with the sun star axis and then measure how far it has to rotate to point at the star, by alternate angles they have then moved through an angle p which is the same as the angle p labelled in the diagram. I was then wondering that if all you had access to was the picture from Jan and July and you could measure the apparent linear movement of the star over that six month period and that you knew what the angular separation of two of the well known stars were in the distant constellation then you could find the angle p that way, or is that what the scientists do anyway? thanks as always, Glenn.