The smallest shift you can reliably measure on the screen is about 0.2 grid units. This shift corresponds to the precision of positions measured with the best Earth-based optical telescopes. If you cannot measure an angle smaller than this, what is the maximum distance at which a star can be located and still have a measurable parallax

The distance is  

Explanation:

From the question we are told that

        The smallest shift is

Generally a grid unit is   of  an arcsec

  This implies that  0.2 grid unit is  

The maximum distance at which a star can be located and still have a measurable parallax is mathematically represented as

substituting values

Note  

So  

answer: its c lololo

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