1psec= 3.26 light years
Russian astronomer Vasily Yakovlevich Struve was able to measure the parallax of several stars
parallax — the angle between the lines Sun — Star and Earth — Star
we can calculate the length of the line Sun — Star
by knowing distance from earth to sun
No trigonometric functions are required in this relationship because the very small angles involved mean that the approximate solution of the skinny triangle can be applied.
a parsec is the distance from which the distance from the Earth to the Sun can be seen at an angle of 1 angular second