The Sundial Page

The aim is to devote this page to developing strange sundials, and displaying unusual designs.

I am particularly interested in vertical sundials, as they can be just plonked on the side of a house. However, to be accurate, the vertical sundial has to be designed from scratch not only for the lattitude, but also for the precise angle of the wall of the house. The calculations are quite evil, but I eventually combined them into a spreadsheet. My father always wanted a sundial somewhere, and after years of trying to persuade the owners of some of the businesses he worked with to have one on one of their buildings, he decided to build one at home. It took about 10 years to invent, develop and finally build the design he wanted. He started from first principles for how his design would create a shadow from a known Sun position, and then I added in the equations for calculating where the Sun would be at times and dates required for the plots to create the shadow lines. To get the most symmetrical and aesthetically pleasing dial, we experimented with different mounting angles until we settled on one, and then he had an entire wall built at exactly the right angle to house it. A new garden wall was needed anyway, but the final position was determined completely by the desired sundial mounting angle! As far as I know, it's unique in that it's a sundial that's see-through and the displayed time is visible from both sides. By their nature, sundials are not particularly accurate, but with careful design and accurate placement (and an accurate list of the Equation Of Time values for each day of the year) we managed to get it down to about 15 seconds which we were very proud of :o)

The sundial is still in place, although the house has changed hands (and name) since then. The pictures below were taken when we'd finished adjusting it, many years ago now.

The garden wall, with Northerly face recessed. The dial is mounted flush on the Southerly face.

"Sol constans est dum terra mondet" - sundials traditionally have latin mottos, this one means "The Sun is constant while the Earth moves".

This is the Southerly side, the Sun casts a shadow of the gnomon onto the dial. The top straight line of the shadow is the time line, and the little hole in the brass "Sun" shape at the tip of the gnomon makes it easier to see the moment when the shadow crosses the hour line on the dial because it has a bright dot in the centre of the shadow. The "figure of eight" plot curve in the centre is an "analemma", which factors in the Equation Of Time and so in this case the bright dot falls on the analemma at exactly Clock Noon (not Sun Noon - Sun Noon is the central vertical straight line). Which side of the figure of eight it lands on depends on the month of the year, indicated along the edges of the dial. It would be possible to create analemmatic hour lines, and even quarter-hour lines, but every feature added to the dial makes it harder to read, so we chose to include just the Noon Analemma. For approximate reading, the Equation Of time data are included on the sides of the dial for a couple of dates each month. The "Sun" gnomon hole is drilled into a little extra bit of metal attached with a screw, which can be adjusted to fine-tune the dial.

Example reading from Northerly face for exactly 9am GMT. Sundials normally read GMT so you have to adjust for that too in Summer, this would be 10am BST.

3D Printed DIGITAL SUNDIAL (also included on my 3D printing page)

A "swiss cheese" of holes in the big gnomon section only allows sunlight through the display slits on the lower flat face at certain times. It reads in 20min increments, so 12:00, 12:20, 12:40 etc. The unit has been entirely precalculated so it just needs to be tilted until the display is brightest, and aligned due North with a compass.

Folds away for neat storage!

THAT'S ALL FOR NOW. Hoping to design a simple vertical dial for our South-ish facing garage which may just be a gnomon mounted above the up-and-over door and some marks on the door for the hour lines. Check back here in a year or several :o)