How to Make a Sundial With a Flagpole

Your flagpole can be a sundial.

You can add interest and utility to the flagpole on your property by turning it into a sundial. According to NASA, in the northern middle latitudes, a sundial with a vertical pointer ("gnomon") will accurately display noon when its shadow is cast north. Telling time accurately using a flagpole sundial is complicated somewhat in that the shadow will drift slightly between the winter and summer solstices. Although not entirely accurate, a vertical gnomon sundial will provide reasonably close readings throughout the year.

Things You'll Need

• Flagpole
• String
• Measuring tape
• One large stone marker
• 12 small stone markers
• Paint

Instructions

1. Secure an 8-foot-long string around the base of the flagpole.

2. Tie a knot in the string 5 feet from the flagpole. You will use this indicator to lay the stone markers in a semi-circle around the gnomon.

3. At noon on a sunny day, place the string along the shadow and put the large stone marker on the shadow at the point where you tied the knot.

4. Place a small stone marker on the shadow that is cast at one o'clock.

5. Continue placing small markers at the 5-foot mark along the flagpole's shadow every hour until six o'clock.

6. Measure the distance between the noon and one o'clock markers. Place the 11 o'clock stone marker the same distance on the other side of the noon marker, using the knot in the string as your guide.

7. Determine the placement of the 10 o'clock marker by measuring the distance between the one and two o'clock stones. Complete the sundial in this fashion.

8. Paint numbers on the stone markers if desired.

9. Observe the shadow on your sundial the next day to make sure the marker placement is accurate, making adjustments as necessary. Once you are satisfied that your sundial layout is correct, remove the string from the flagpole.

Tips & Warnings

• If your flagpole is in a paved area, you can draw a chalk circle 5 feet away from the pole. Every hour, simply place a marker where the shadow crosses the chalk line.

References

• NASA: The Sundial
• MySundial: The Sundial Primer

Resources

• North American Sundial Society: Sundial Construction
• Sundials: Six Sundial Projects
• LORIA: Three Dials, and a Few More