This photograph shows the beginning of a new project next to Keppel Henge that started in November 2009. We've used the Keppel Henge site to create an analemma in the sky, and now with this disk we will be creating an analemma pattern on the ground.

The large disk at the end of the pole in the photograph has a hole in the centre. Each sunny day, at midday, the Sun shines through the hole and makes a bright spot on the ground. At exactly 12:22 p.m. local standard time we place a marker on the ground in the centre of the bright spot. Gradually, day by day as the spot changes its location, an analemma pattern is traced out on the ground.

The disk is about 5 meters above the ground, and it is tilted on a 45 degree angle to match our local latitude.

This shows what the hole, or aperture bright spot looks like. We are hammering in short lengths of rebar to mark the centre of each day's bright spot. The time 12:22 p.m. was chosen since it is close to the yearly average transit time of the Sun at our location.

During the winter months the spacing between the marks was about 4 cm. from one day to the next. It wasn't too difficult dealing with the winter weather while locating the markers. There were only a few times that we had to use snowshoes to get to the site, and we only had to shovel down through the snow to ground level a dozen or so times. The biggest problem was a long cloudy period from late December into January when we couldn't place any markers.

We were surprised to see that the distance between the winter solstice marker and the spring equinox marker was 6.7 meters — quite a distance! In the early spring, the distance between markers from one day to the next had shrunk to about 2 cm.

Shortly before the Summer Solstice the pattern took a sharp turn inward as it reached its end point, and the Sun was at its greatest altitude for the year.

At this time of year the day to day markings were so tightly packed that they touched each other, and we began to place markers every other day to give them some space. Once the solstice has passed, the pattern begins to move north again (for the first time since late December) and it will curve back to complete the analemma.

On the day of the Summer Solstice a group of about thirty-five people gathered at Keppel Henge to mark the occasion. We talked about the history of the henge, and how it works. Some members of the Bruce County Astronomical Society brought their solar telescopes, and we were able to observe the surface of the Sun.

We also had a look at how the pattern was developing after the Summer Solstice marker was put in place — a long distance from the Winter Solstice marker!

Once the pattern is complete we plan to construct a small wall that follows the marked pattern. If all goes well we should be finished in late 2010.