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  • Writer's pictureEvan Boxer-Cook

This Sundial Has a Lot of Style

Updated: Oct 5, 2023

Two of them, in fact


The video below offers a demonstration of the effects of a wide gnomon on horizontal sundials.


When the gnomon of a dial is of significant width, the hour plate must be split at the noon mark and pulled apart so that the mark for noon is as thick as the gnomon is wide (the noon gap). This is because a gnomon of this size effectively acs as two, with each edge casting the time-indicating shadow for part of the day before handing the task off to the other.


Style Tradeoff

The shadow-casting edge of the greater gnomon is called the style, and because this dial has two, certain allowances must be made as mentioned previously.


Keep in mind that because the rays of true sunlight are parallel (unlike the diverging rays from a flashlight), the shadows in these models do not exactly reflect those seen on real sundials. For example, noon on a real dial would be marked by a northern shadow of equal width to the gnomon with parallel sides. In the model, the shadows of the styles diverge instead.


The wider the gnomon, the easier it is to demonstrate the effects of a double style. As seen below, the early morning sun projects the eastern style;


the 6 AM sun projects both styles;


and the mid morning sun projects the western style.


At noon, both styles are projected north, thus necessitating the noon gap for a precise reading of 12.



In the afternoon, the styles switch off again as before.





Here, the full day of style switch-offs can be seen:


The wider the gnomon, the wider the noon gap and the easier it is to observe the switching style.

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