Polar distance (astronomy)

From Wikipedia, the free encyclopedia

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:

[edit] Definition

Polar distace (PD) = 90° ± δ

Polar distances 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.