Parallax Method Formula — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Parallax Method Formula Used primarily in astronomy to determine distances to nearby stars, and in terrestrial measurements for inaccessible objects. Visualize a triangle formed by the two observation points and the distant object. Assume the object is the center of a circle with radius D (Distance). Treat the basis b as an arc length on this circle. Use the definition of angle in radians: theta = arc / radius. Substitute variables: theta = b / D. Rearrange to solve for D: D = b / theta. The angle theta must be in radians. The formula assumes the distance D is much larger than the basis b (D >> b), allowing the small angle approximation tan(theta) approx theta. Substituting the angle in degrees or arcseconds directly without converting to radians. Confusing the parallax angle with the full angle between two lines of sight if the convention defines theta as the semi-angle.