What is the parallax formula and how is it used to calculate . . . - Toppr The parallax formula states that the distance to a star is equal to 1 divided by the parallax angle, p, where p is measured in arc-seconds, and d is parsecs d = 1 p Explanation: Parallax is a method of using two points of observation to measure the distance to an object by observing how it appears to move against a background