Jeff Adkins wrote: > > > Hi, > > I'm new to the list too. But I'll attempt to answer your questions. > My responses are preceded by -- > > Jeff Adkins > [EMAIL PROTECTED] > > rodandkellyheil wrote: > > Secondly, how does one construct a gnomon for an equitorial > sundial which adjusts for the equation of time? > > -- I don't think anyone tackled this, so here goes. > Since the equation of time causes the sun's apparent > rotation around the gnomon to vary in angular speed, there > isn't anything you can do to the gnomon to compensate for > that in a standard equatorial design. I assume you are > attempting to make the sundials' display of local solar time > begin to approximate standard time like on your watch; i.e. > you could set your watch with it. > > There are two ways (at least) to compensate for the equation > of time: One is to make an absolutely perfect dial with 15 > degree increments (offset properly for your position within > the time zone), and simply subtract or add the equation of > time values from what the clock displays. Another is to > make the equatorial dial moveable--with a small index mark > labeled with positions corresponding to the equation of time > on various dates, say one for every month or every two > weeks. The sundial instructions would then read: > > "Rotate the dial clockwise or counterclockwise until the > index mark matches the date. Then the clock will read the > corrected time." > The pattern of dates will resemble a squashed analemma of > the correct size in relationship to the circle--for example, > a 15 minute offset would be 15 minutes*360 degrees/(24 hours > x 60 minutes) or a little less than 4 degrees. >
Hello all, This answer to the question if a gnomon could be made for an equatorial sundial which adjust for the equation of time isn't fully correct, because such a gnomon can be made. One solution is a solid body shaped as the half of the EoT curve mounted to the gnomon, one for each half year. The other is a plate in which the EoT curve is cut out. For this solution see Compendium, bulletin of NASS, vol. 5, no. 4 dec. 1998 Happy dialling, Fer. -- Fer J. de Vries [EMAIL PROTECTED] http://www.iaehv.nl/users/ferdv/ lat. 51:30 N long. 5:30 E
