Explain what is Parallax and Distance Measurement?

To measure the distance to nearby stars, astronomers use an effect called Parallax.  Parallax is the apparent displacement of an object because of a change in observer’s point of view, for instance, when we look at object with one eye shut and then doing the same with other eye, there is a difference in the position of the object this is known as Parallax.

To measure the star position astronomer uses this technique. Once the star position is located after six month they will again calculate the apparent change in position.