How is the angle used for parallax found?
3 Answers
It’s measured against a “fixed” background of distant stars/galaxies that are assumed to be immobile.
Explanation:
From our perspective the position of a nearby star ‘jumps’ when viewed 6 months apart against this distant background. That jump is expressed as an angle, and then converted to a distance by trigonometry. For objects closer to us a shorter baseline than the diameter of the earth’s orbit is possible - see here:
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It can also be measured due to the sun’s motion around the galaxy:
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Is this a more useful answer?
It’s now occured to me you might have been asking ‘how physically do you measure an angle in space?’
Explanation:
Two methods: using the known gearing mechanism on the telescope or (in simpler amateur devices) you can get a graticule on the eyepiece.
