The proportions of an analemmatic sundial are determined by the latitude of its location. Each design is unique as a result. Simple equations are used with your local latitude to give a set of values for all of the hour stone placements. Our first step was to make a small paper mock-up which was used to test the design for accuracy. A pencil was used as a gnomon.
We decided on a width (the major axis of the ellipse) of 6 meters. Using a compass we carefully aligned the minor axis of the design with our meridian and then measured out the major axis at right angles to it. The hour points themselves were located by measuring out along the semi-major axis from the centre point, and then up or down by a distance determined by the equations in step one. We used wooden stakes to temporarily mark the location of each hour point.
The next step was to build a wooden frame and pour the concrete for the date scale. Before the concrete set, we placed a small ceramic plaque in each square to indicate the month. The months of June and December are at either ends of the date scale and they are quite narrow compared to the other month squares since the sun's apparent elevation in the sky changes very little as it passes through the summer and winter solstice. Once the concrete had set we tried out the sundial to see if any adjustments were needed to the hour points.
The hour point positions checked out fine so we replaced the wooden stakes with the permanent hour stones. A wooden frame was built that followed the curve of the ellipse and the hour stones were set in concrete. We started with a 5 cm base of coarse concrete to hold the stones in place. Reinforcing rod was put on top of this first pour.
A 5 cm layer of fine textured mortar was then poured on top of the coarse mix. As we worked around the ellipse, we made a ceramic mosaic pattern around the hour stones. Steve is a potter so fortunately (or unfortunately!) he had lots of broken pottery shards at his studio to use for the mosaic.
This over view photo shows the sundial nearing completion. The wooden form for casting the concrete has been moved along and is being lined up for the final section. The sundial is set to Daylight Saving Time since during most of Standard Time, November to April, the sundial is under snow and not in use some winters there can be much as 16 feet of snow at Keppel Henge!
|Home Pg 2 Pg 3 Pg 4 Panorama Analemma Eclipse Sundial Solar System Aerial Pinhole Flare Star Trails Solargraph Analemma Pattern Contact|