HORIZONTAL SUNDIAL BUYER’S GUIDE
Five Golden Rules to check before you buy
Most sundials for sale in garden centres aren’t worth bothering with - the manufacturers don’t seem to know what sundials are all about. However, there are some quite reasonable ones to be found, so here’s a short guide of what to look for in a horizontal sundial
Firstly, is the gnomon perpendicular to the dial and pointing in the right direction? The top should be pointing towards the 12 noon mark. Some makers design their sundials for Summer Time, so in that case, it will be 1pm at the top rather than 12 noon. It may not always be the maker’s fault. If they are shipped flat, the retailer may have put the gnomon on the wrong way
Next, are both sides of the gnomon straight? I’ve seen many a curved one, and even a spiral one! They have to be straight, otherwise you don’t know which bit of the shadow to read.
The angle between the face of the sundial (the dial plate) and the gnomon should be equal to your latitude. For UK buyers, London is about 51º and Edinburgh around 56º. You can find your latitude from most maps.
The gnomon has thickness. The shadow comes off different sides of it as the day progresses. There should be a gap, called the noon gap, to allow for this change, and it should match the thickness of the gnomon.
Finally, check that the point where the gnomon edges join the face of the sundial meet up with a line that joins 6am and 6pm .
If the sundial is designed for Summer Time, this will be the line joining the 7am to 7pm lines, of course.
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