Cylindrical sundials


There are many kinds of cylindrical sundials, but the most popular is maybe the cylindrical shepherd's dial although armillary rings are also quite common.

The cylindrical shepherd's dial

The shepherd's dial is a cylinder with a rotating hat on top, equiped with a perpendicular style. The dial is held vertical by a ring or a cord, and the hat shall be rotated to the mark of the day. Then the dial is oriented so that the style points towards the Sun (while the dial stays vertically). The shadow casted by the style will fall on a curve that tell the solar hour. Time is therefore given by the Sun's altitude.

The program Shadows allows you to print the layout of hour curves and date lines. You just need then to fold the paper around a cylinder and add a rotating hat and a style.

   

The armilary ring

   

The armillary ring is in fact the equatorial band of an armillary sphere. The style of this sundial is made by the pole axis of the sphere. This axis cast a shadow on the equatorial band which is scaled in hour angle, with 15° per hour. Several parallel line can be drawn to scale the Sun's declination. Each hour line can also be replaced by an analemma curve (8-shape) to provide mean time instead of solar time.


The polar cylindrical sundial without style

This sundial is built inside a semi-cylinder which axis is parallel to the pole axis (i.e. a polar sundial). The shadow is casted by one of its edges, for example the right edge during the morning, and the left edge during the afternoon.


The vertical cylindrical sundial

This dial is drawn outside a vertical cylinder. The style is installed perpendicular to the surface, and oriented towards any azimuth. This dial can be installed for example on a cylindrical tower.

 


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Photos:
- armillary ring: Precision Sundial © Hoffmann Albin, www.precisionsundials.eu
- armillary ring (detail): photo Helga Nordhoff, Visit his Web site - armillaire sphere: windchimedirect.com