Hi Alex, Great idea, although I can't help wondering why anyone at Burning Man would need, or even want, to know the time that accurately!
How big do you want your dial to be? Burning Man would be a great place for a monumentally big one. Frank King's suggestion needs a different set of lines for every few days so might be difficult to scale up. With a triangular gnomon you only need one set of time lines. During the last two weeks of August the sun goes from being 4 minutes slow to a few seconds fast. So, if you mark the dial for a date in the middle, your dial will go from 2 minutes slow to 2 minutes fast. That's within your +-2-3 minutes goal. In any case, the shadow is fuzzy and it's difficult to estimate its edge to better than about a minute. I'm sure people would be impressed by a sundial that is that accurate. That's if they've got their watches on. That's if they've got anything on. Marking the time lines requires that they all be calculated, or marked out on the first day. If you do mark them out on the first day, bear in mind that the sun will get faster during the two weeks, so mark them about 2 minutes late. For instance, mark noon when your watch says 12:02. An alternative that is little known is achieved with a gnomon that sticks up, but not straight up, nor at the angle of your latitude but exactly half way between these angles. The beauty of this is that the hours become equally spaced, at 15 degrees per hour (and 4 minutes per degree), so it is much easier to mark them out. The only complication is that the circle of hour lines isn't centered at the foot of the gnomon but a short distance away. That distance is easily calculated but does change a little with the date, so either the dial or the gnomon would have to be moveable to maintain full accuracy. Another alternative, that might well appeal to Burning Man people, is a sundial that doesn't tell normal time, but does accurately tell you how long it is until sunset. Such a sundial would surely be more of a talking point. The desert is an ideal place for it as it is very flat, so the true sunset is near enough at the theoretical time when the sun goes below the horizon. Also, I bet it gets dark very quickly after sunset, so it's an important time to know. These sundials don't suffer from the Equation of Time, so they are accurate all year. If you're interested, I can post design ideas. Chris Lusby Taylor 51.4N, 1.3W ----- Original Message ----- From: Alex Botkin To: sundial@uni-koeln.de Sent: Monday, September 29, 2008 3:37 AM Subject: Temporary sundial Hello to all, I am contemplating a temporary sundial sculpture. It will be in its location for about two weeks maximum the last weeks of August. Long -119.22 Lat 40.76 That's the middle of the Black Rock Nevada desert. I'm not knowledgeable enough to even be considered an amateur, so apologize in advance for the simplicity of my questions. Could I erect a vertical gnomon and mark the hours as they occur based on a watch set to local time? (The children's Plunger learning project suggested this to me) Would this maintain accurate mean time (+- 2-3 minutes) during the duration of its service? Using the coordinates, I have plotted a triangular gnomon (using the free Shadows 3.0) . If I kept the angle of the gnomon as plotted would I be able to mark hours (as above ) ? Thank you, Alex ------------------------------------------------------------------------------ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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