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The gnomon casts a broad shadow; the shadow of the style shows the time.
The gnomon may be a rod, wire, or elaborately decorated metal casting.
Sunrise and sunset occur at 3am and 9pm, respectively, on that day at geographical latitudes near 57.05°, roughly the latitude of Aberdeen, Scotland or Sitka, Alaska.
The Earth rotates on its axis, and revolves in an elliptical orbit around the Sun.
The sundial's indicated solar time thus varies from clock time by small amounts that change throughout the year.
This correction — which may be as great as 15 minutes — is described by the equation of time.
The style's angle from horizontal is equal to the sundial's geographical latitude.Planes are the most common surface, but partial spheres, cylinders, cones and other shapes have been used for greater accuracy or beauty.Sundials differ in their portability and their need for orientation.To obtain the official clock time, three types of corrections need to be made.Firstly, the orbit of the Earth is not perfectly circular and its rotational axis not perfectly perpendicular to its orbit.