Question

In parallex method, we observe a star at a particular point from earth, till the time we reach diametrically opposite point on earth's orbit does that star remain at that point and at second observation there are too many stars how do we came to know, which star we measured before?

Answer 1

In reality we never measure the distance of a star by using parallax method.
The situation discribed is only meant for understanding the concept and doing problems.


In reality the scientists use a class of variable known as Cepheids, which pulsate in and out like beating hearts. There is a direct relationship between the length of a Cepheid's pulsation and its true brightness. Measuring a Cepheid's apparent brightness -- how bright it looks from Earth -- allows astronomers to calculate its true brightness, which in turn reveals its distance.This allows them to calibrate a Cepheid's true brightness, which then can be used to calculate its distance. Cepheids are especially bright stars, so they are visible in galaxies that are tens of millions of light-years away..