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Polar DistancePolar distance (PD) is an astronomical term associated with the celestial equatorial coordinate system Σ(α, δ) and it is an angular distance of a celestial object on its meridian measured from the celestial pole, similar as declination (dec, δ) is measured from the celestial equator: - PD = 90° δ .
Polar distance are expressed in degrees and cannot exceed 90 in magnitude. An object on the celestial equator has a PD of 90. Polar distance is not affected by the precession of the equinoxes. If the polar distance of the Sun is equal to the observer's latitude, the shadow path of a gnomon's tip on a sundial will be a parabola; at higher latitudes it will be an ellipse and lower, a hyperbola.
In geometry a polar distance, typically denoted r is a coordinate in polar coordinate systems (r, θ) and (r, θ, h). The distance d between two points P1 and P2 with their polar coordinates (r1, θ1) and (r2, θ2) in two dimensional circular polar coordinate system is given by the polar distance formula: - .
Polar distance is used also in botany in classification of pollens.
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