The closest star to the solar system is Proxima Centauri, whose parallax is 0.76 arc seconds.Measuring the parallax of a star, it is only necessary to calculate its inverse to have the distance in parsecs.Īnother possibility is to define a parsec as the distance at which two objects, separated by one astronomical unit, appear to be separated by an angle of 1 arc second. Where Δ is the distance in parsecs and β the parallax in arc seconds. That is, at double Δ, π becomes half but if Δ is half, π will be double, and so on, in such a way that the relationship between distance and parallax becomes very simple: Δ = 1 b Now, since β (read beta ) is a very small angle, on the order of up to one thousandth of an arc second, it will behave as a linear function of inverse proportionality with respect to Δ (read delta ). Since the parsec is a distance related to the astronomical unit, it is related to the tangent of the angle at P (see diagram). It is based on the trigonometric parallax method, the oldest and most widely used to determine the distance to stars. Parallax is measured in arc seconds (60 arc seconds = 1 arc minute 60 arc minutes = 1 degree). The basic separation used by astronomers to determine the parallax of stars is the radius of the orbit of the Earth.

Parsec definition