Polar 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 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 systemss (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.
