Areading may appear to be different when viewed with one eye or the other, or when the head is moved from side to side or up and down. this apparent measurement difference is due to a change in position of the observer, and is called

a. extrapolation
b. interpolations
c. parallax

Answer : Parallax

Explanation :

The difference in the position of an object when viewed from different points is called Parallax.  

The principle of parallax is used by the astronomers to find the distance of a planet or a star from earth.

A baseline of 1 astronomical unit is used by astronomers to find the distance between the stars and the earth.  Also, they measured tiny angles in arcseconds.

By doing calculations they found the distance of a star from earth is about 93 million miles or 150 million kilometers.

So, the correct option is (C).