Hi Dave, Yes, your suggested procedure for using sunrise time to determine the marker point for an existing analemmatic dial is correct. Again, it will work for any date, but the error is minimized by using the solstice. Use the other simple sunrise equation below to calculate the time of sunrise, when the solar altitude is zero.
Cos(t) = -Tan(Dec) * Tan(Lat) I had to check my sunrise tee shirt to confirm this equation. This solves for the time angle from solar noon. Convert this from degrees to hour and minutes from noon by dividing by 15. This applies for a dial with no longitude correction built in. Roger Bailey Walking Shadow Designs N 51 W 115 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Dave Bell Sent: January 11, 2002 12:18 PM To: Sundial Mail List Subject: Re: Seasonal Sunrise Marker 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
