A great time for Sundials

Sundials have fascinated astronomers for centuries.  Stargazers have since moved on, but the sundial still remains a popular phenomenon.  Understand this time piece by diving into how it works.

Sundial Vocabulary
Even the most casual reader must become familiar with the three main components of every sundial.

Gnomon:  Pronounced like "no mon", this part casts a shadow on the sundial to indicate the time. 

Dial Plate:  The "clock" part of the sundial where the shadow from the gnomon lands.  Hours are marked on this face.

Dial Center:  All hour lines meet here, usually at the northern base of the gnomon.

Sundials can be much more complicated, but all share these basic parts.

And the moving part
Sundials have a moving part-the Earth!  As our planet rotates, the sun moves across the sky.  Sunlight hits the gnomon, casting a shadow onto the dial plate.  Wherever the shadow lands, that's the hour.

Types of Sundials
Since the earth's axis is tilted, the sun's path across the sky changes by the day.  That means the accuracy of sundials is compromised.  To compensate, several types of sundials have developed over the centuries, the major differences are on their dial plates.

Horizontal Sundial:  Most common for gardens and parks.  The dial plate is flat and the gnomon aligns to that location's latitude.

Equatorial Sundials:  On these sundials, the dial plate is parallel to the equator, and the gnomon is set perpendicular to the plate.

Polar Dials:  The dial plate on these sundials rest parallel to the earth's polar axis.

Analemmatic Dials:  An interactive sundial where you act as the vertical gnomon.

A Sundial for You
Setting up your own sundial is a bit more involved that just putting it outside.  The sundial must face north, and the gnomon must rest at an angle equal to your latitude.  Instructions included with sundials will provide specific directions for use.

Sundials are made of different materials in a variety of sizes.  A great traditional Egyptian sundial is great for yards.  For something a bit more fun, try a peacock sundial.  Prices range from a meager $30 to as much as you wish to pay. 

More information on sundials