Dear Art: You know Art, you really write GREAT answers!
Let me go through them to see if I understand correctly. >Solution A and B both suffer from the difficulty of properly orienting your >auxiliary system. How will you know where the axes of your protractors are? >(I'm not sure what you had in mind, but I imagine two or three distance >measuring devices with fixed axes.) I thought that I could use either or both of the methods described by Mayall pg.75-77. I'll call these" the concentric circle method" and" the apparent noon method" Wouldn't both of these methods show true north very precisely if the vertical gnomon was very tall? How will you orient unit squares >north-south, make sure they have right angles, and mark off the units? Once I know the true meridian, all of the right angles to it are easy to mark using plane geometry. I would probably use the frame &( x,y) coordinate system proposed by John Pickard and Francois Blateyron for plotting. These >problems are in addition to the questions of whether your surface is really >horizontal and whether your giant gnomon was really mounted in the proper >position. Well, I will certainly take great pains to see that this does not happen! Using water level as a guide, it is possible to produce a perfectly level surface. )This is how the egyptians leveled the base of the pyramids. If I orient the azimuth of my gnomon using Mayall's methods, and I know that the face is level, then using simple geometry, it is easy to set it at the proper angle or height. Of course, if you use a cable or edge as your gnomon, and it is >not oriented parallel to the Earth's axis you will always have some errors, >but these can be minimized and all the rest eliminated by method C. Almost everyone in the group agrees with you on this point. There's nothing like the real thing! Solution >C takes a lot of calendar time if you use it to extract seasonal as well as >diurnal information, but I would at least use measurements spread over a day >to orient the gross grid and then use mechanical or optical methods to fill >in the details. But which day of the year is the best for doing this? Please tell me if I'm wrong in my thinking, but wouldn't you want a day where EOT=0 because then you could quickly mark the timelines by a clock without corrections. (I suppose you could also set the clock off by the EOT amount on the day of hour line marking). This would give a longitudinally corrected dial. You would also want to do it near the solstices when solar declination is changing the least. Right? So the best day of the year would be Dec. 25. What do you think Art? Is this correct? Maybe you really have a combination of methods in mind >anyway, since, if you really meant "protractors" in Solution A, then you >must be presuming that you have already determined the north-south line. > >Isn't a giant protractor just a piece of non-stretchy string? No, a piece of non-strechy string is just drawing compass that hasn't been nailed down yet! Thanks again, Art John Carmichael
