The correct answer is Parallax Method Explanation & Key Takeaways: Parallax Method • The distance of stars or planets from the earth is very large. • These distances cannot be measured directly with a scale. • To measure such distances parallax method is used. Parallax: • The apparent change in the position of an object because of a change in the position of an observer is known as parallax. • To measure the distance of far away situated star or planet we can do the following steps. • We observe the star from the earth at a certain time. • We again observe it after 6 months when the earth completes its half revolution. • We also measure the angle between these two directions along which two planets are viewed the angle is known as Parallax Angle. If S is the position of the object and A B are the two points of observation, \(\theta =\frac{b}{D}\) • Similarly, for a planet, if d is the diameter of the planet and α is the angular size of the planet \(α =\frac{d}{D}\) This shows that the parallax method is used for measuring the distance of stars.