How to Calculate Sundial Coordinates

Though easy to make, sundials require specific alignments and coordinates.

Sundials are ancient time-telling devices that work based on the sun's journey through the sky. The sun casts a shadow upon a sundial pointing to an inscription informing the viewer of the time of day. Of course, its dependence on the sun makes this device useless at night or at times when the sun is somehow blocked from view. Learn the basic theory behind a sundial's coordinates before building one of your own.

Instructions

1. Find your location's latitude. The angle that equals a given time on your sundial will depend entirely on the latitude of the location at which you plan to place it. This fact holds true of every hour of the day except for 6 a.m. and 6 p.m., which are both always at zero degrees. You must then print these angles on the face of the sundial to allow the shadow of the sun to point to a specific time. The face can have any style or shape, but the angles must remain consistent.

2. Create a gnomon, the angled dial in the center of the sundial. Like the angles on the face of the sundial, the gnomon's exact angle depends on the location's latitude, which represents exactly the degree of angle the gnomon should have. Austin, Texas, for example, is at 30 degrees latitude, so the gnomon of a sundial in Austin would have a 30-degree angle. The gnomon always faces 12 noon on a sundial's face.

3. Build your sundial. Note that the materials you use will not affect its accuracy. Sundials can even incorporate paper or cardboard. More permanent sundials are made of more sturdy materials such as metal or wood. The calculations of time and gnomon angle will always remain consistent regardless of the materials.

4. Align your sundial north. The gnomon should be in line with the north and south compass directions with 12 noon pointing due north. Place the sundial in a location that receives as much sunlight as possible so it can show the time as effectively as possible. The gnomon must be in line with 12 noon, which must in turn point directly north; otherwise, the times reflected on the sundial will be incorrect.

References

• Hila Road; Hila Sundial Hour Line Calculator; Wayne Campbell