Article of the month March

Paper model of a horizontal sundial

This is a paper model of a horizontal sundial for the Netherlands.
The sundial is drawn for 52 degrees latitude.
Save the graphic below and print it on somewhat heavy paper, say 120 grams.

Cut out the circle as well as the centre-pointing wedge marked W. That is all the cutting required.

The two hour lines marked X are valley folds, the dotted line Y is a mountain fold.
Score them which with the back of a knife for easier folding.

Fold the sundial and glue the backs of the style triangle together.
The result should look like the second figure.

Place the sundial horizontally in the sun with the style pointing north.

Model
Save and reopen in your own application for a larger picture

This model shows local apparent time. It reads noon when the sun is exactly south.

To convert LAT to civil time, two adjustments are applied.

The first, the longitude adjustment, is a location constant.
For the Netherlands, this adjustment is 4 × (15 – east longitude) minutes, to be added to the dial reading..
When summer time (daylight saving time) is in effect, an extra hour is to be added.

The second adjustment, the equation of time, depends on the date. It is subtracted from the dial reading. .
There is an equation-of-time table for download on this site.
Pay attention to the plus or minus sign of value.

Remarks.
The angle between the lines marked X equals twice the design latitude.
With the model folded up, these lines form the local noon line.

Within the Netherlands, moving to a different latitude will hardly affect the accuracy.

This sundial, made for the Netherlands, will work whenever the sun shines.
In higher latitudes, there may be more hours of sunshine. When the dial is made for those locations, its construction limits the number of useable hours.