On Fri, 11 Jan 2002, Roger Bailey wrote: > The seasonal sunrise marker is a point on the east west axis of the > analemmatic dial that is used in combination with the date line of the > Zodiac table to show when and where the sun rises throughout the year. Stand > on the sunrise marker point and view across date marks on the zodiac to see > where the sun will rise on that date. Or stand on the date mark on the > Zodiac and view past the sunrise marker to see the time of sunrise on that > date. Use a string from the date through the marker to the hour ellipse to > convert the dial into a sunrise calculator. What could be easier? > > Here are the steps to calculate where to put the seasonal markers on any > analemmatic dial. All you have to do is determine where the red line crosses > the axis. This calculation could be done for any date but the error is least > if you use the solstice, either the summer or winter (they are symmetrical). > > 1. Calculate the azimuth of the solstice sunrise for your latitude. When the > altitude is zero (sunrise), the azimuth (Az) given by Cos (Az) = Sin (Dec) / > 2. Solve the right angle triangle between the two axes and the red line to > find the marker point on the E/W axis. Start with the zodiac distance on the
This is a marvelous "new" use for an analemmatic dial, for sure! I truly wish I had a nice, large, flat piece of land on which to build one. Looking at your instructions (partially clipped, above), I assume they are for the case where one only wants the markers. If the analemmatic dial already exists, simply consulting an almanac for the rise and set times on the desired dates - or presumably, on ANY one date - should let you pull a string from the date point to the time point, and mark where it crosses the East-West axis. Yes? Dave 37.29N 121.97W
