Polar sundial

from Wikipedia, the free encyclopedia
South polar sundial
(polar) east sundial

A polar sundial is a type of sundial in which the dial contains a parallel line to the earth's axis . If a pole rod is used as a shadow thrower , it is parallel to the dial, its shadow lines are parallel to it and to each other. So they do not intersect at one point, but are arranged like the rungs of a ladder - but with unequal distances between them.

Polar south clock

With the polar south clock , the normal of the dial is in the meridian plane . The marking of the noon shadow is located directly under the pole rod. The remaining hour lines have the distance   c = d · tan (τ)   ( d is the distance of the pole rod over the dial, τ is the hour angle of the sun). The dial is typically scaled from 7 a.m. to 5 p.m. ( true local time ). The displays for 6 o'clock and 6 o'clock are not possible because the shadow of the pole rod at these moments would theoretically be infinitely long.

Polar east and west clock

Multiple sundial in Steinfeld Monastery (Eifel) . Front: (polar) east clock with parallel lines; then: north-east clock; right: north clock; left: south clock; then: south-east clock; above: horizontal sundial;

The (polar) east sundial (the normal of the wall points to the east: "east wall") or the (polar) west sundial (normal points to the west: "west wall") are created with other special positions of the dial . With the east clock, the scaling usually ends at 11 o'clock, with the west clock it starts at 1 p.m. In both cases, the shadow at noon would theoretically be infinitely long. The distance of the hour lines from the line directly under the pole rod is c = d ÷ tan (τ) (line under the pole rod for 6 o'clock in the morning or at 6 o'clock in the evening).

The polar east and the polar west sundials are mostly only referred to as east and west sundials because they are also special cases of vertical sundials.