Question

The apparent change in position of a Star when seen from opposite sides of earth's orbit is called

Answer 1

Parallax es la respuesta. :)

Answer 2

"Parallax shift".

We can't SEE the difference in position of any star as seen from the Earth 6 months later or earlier, but by measuring the very tiny differences in the positions of the more distant stars, we can observe the "parallax" of a star and thus calculate its distance. This only works for stars less than about 300 light years from Earth.