Sunny Day! It was a bright sunny day here in the Great White North. Sunny because it was about minus 29 degrees C.
I went to the shed and got a couple of sticks, one being the handle from an old broom and the other from a rake. I am sure that most of you have done similar experiments. I stuck the broom handle vertically in the snow and the rake handle on a slant. The contrast of the shadows against the white snow was excellent. I have included a couple of pictures. Almost froze the fingers on my right hand getting these. Pic_1 was taken at the base of the sticks and shows how sharp the shadows are. Pic_2 shows the ends of the shadows. They are becoming very fuzzy. It is possible to determine the centre of the shadows but finding the edges is not an easy task. Zoom in and you will clearly see the. It was also obvious that the stick's shadows tapered significantly as you get further away from the base. Is this taper always the same? Probably not. It is also very difficult to find the tip of the stick's shadow. It is not where you think it is. And sometimes it is totally lost in the shadows. The longer the shadows become relative to the length of the stick the less distinct the shadow is. I viewed the shadow from a thin wire rod on the snow and very quickly there is no distinct shadow at all that could be used. I imagine these are the same issues that would be experienced in the design of a monumental sundial using a rod gnomon. If the rod casts an extremely long shadow and you must use this shadow to tell the time there will be a point where the shadow is no longer useful. I would think the gnomon should be relatively long in comparison to the size of the dial plate to provide good shadows for reading. Having an extremely large sundial using a shadow casting gnomon and making it very accurate are probably mutually exclusive. There is no doubt a limit to the size of a sundial that will allow it maintain its function at a particular location for the entire year and for all times it is illuminated. So if its big it better be spectacular so people don't really notice that it isn't working that well. Like the Sundial Bridge. This would also apply to a nodus. I would guess John that your sundial at the Colorado school might be experiencing this. I believe its gnomon ends at a tip. I believe the shadow of this tip may be lost in the shadows at this time of year. If not it would be interesting to know as the sundial is quite large and also a bit further south than my handles. There is a 60 metre horizontal sundial located in Lloydminster Alberta/Saskatchewan in Canada. It uses a rod gnomon but I have never seen it and do not know how well it works. It appears to have only the full hour lines so the designer may not have been trying for the accurate indication of time. It is simple but impressive because of its size. You can see it at: www.mts.net/~sabanski/sundial/sotw_canada_lloydminster.htm Anyway, biggest is not always better. There must be a balance between the form and its function. A monumental sundial need not be the biggest sundial. If you have a sundial, large or small, that you have built or are involved in building share it with the rest of us. It will help to motivate others to try to build their first sundial. Happy Dialling! Carl Sabanski www.mysundial.ca
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