Sundials are ancient timepieces that rely on light from the sun to give structure to the cycle of your days in a garden setting. An ideal sundial is aesthetically pleasing and custom designed for your specific location (in this case, Dallas). Landscape design materials like cast iron, aluminum, bronze and stone are all suitable for constructing a “timeless” sundial that will last for decades.
Basic Sundial Design
You can make a sundial from a traditional design if you are using it for purely aesthetic purposes or to tell “Local Solar Time”. The principles involved in building such a device are fairly simple. However, how we calculate time today introduces complexities that can require additional features for real accuracy. For example, you might wish to calibrate your sundial to Central Standard Time or Daylight Savings Time.
All sundials have certain parts in common. These can be creatively developed so they match the overall look/feel of your Dallas landscape design. The surface on which the shadow is cast is known as the dial plate. It can be a flat plane, conical or hemi-spherical shape (either convex or concave).
The gnomon is the physical structure that casts the shadow. It can be a simple triangle, a rod, or a more elaborately carved shape as long as the shadow-casting edge (called the style) is straight. If just the tip rather than the full blade edge of the style is used to tell time, this is called the nodus.
Declination lines are the hourly time positions mapped out on the dial plate as the shadow from the style indicates. Unlike clock hours, the intervals marked on the plate are unequal on a horizontal garden sundial. Sound complicated? Don’t worry. There is free software available to help you figure this out. Or, you can custom order a sundial.
Location Equation
The map coordinates of your location will determine the exact position of the hour markers. The latitude (your distance from the equator) is the primary concern when making the apparatus accurate for telling local solar time. For the DFW area, this calibration needs to correspond to about 32° N.
Time zones each cover 150 of the circumference of the globe out of a total of 3600. This means your longitude (how far east or west you are from the centerline of your time zone) impacts the accuracy of your time piece. You can correct your sundial design to account for your precise longitude (Dallas is at 96° W). However, it will still vary plus or minus 16 minutes from CST throughout the year for reasons that are more complex.
Adding Furniture
Dial “furniture” includes all the extra indicators or features engraved on the dial plate. The equations that allow you to figure out the exact CST from the date and the local time showing on the sundial can be included here. You might also choose more decorative furniture such as the zodiac signs or the points of the compass.
Installation Considerations
When the sundial is ready to be mounted on site, point the gnomon toward the North Star. Also, use a plumb line to ensure the plate is completely level. Choose a location that is not shaded during the day. If you select an elegant design with a pedestal mount, this can serve as a focal point for your entire landscape.