Polar distance

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 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 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.