An exciting new installation is taking place on the grounds of the MARBLE/marble symposium: an Analemic Sundial. Most 'garden variety' sundials are off by as much as 15 minutes in either direction and require an accompanying correction graph plotting "the equation of time." An anelemic dial incorporates this sinusoidal correction thus obviating the need for a separate graph. A well-designed analemic dial can be read accurately to within about two minutes year around. An anelemma is often printed on the side of globes.My first exposure to analemic dials was from an article in Scientific American back in the 80's. I immediatly began programming my own dial generator using "Rocky Mountain Basic" on an HP9845--a very cool desktop computer (technical desktop version of the HP 300) which predated MAC's and PC's.
Our Crystal River sundial is to be engraved on a slab of marble also serving as a coffee table overlooking the Crystal River (see photo below). Without a perfectly flat and perfectly level (or known orientation), computer-generating the dial is out of the question. Instead, we've embarked on an emperical approach using a radio-controlled clock, a hammer and a chisel. Over the next month, during the three sessions of MARBLE/marble (July 2 - August 5), passers-by will be placing tic marks on the quarter hour. Next year at this time, we'll hopefully have enough data to carfully and elegently carve the hour lines into the table as well as add other decorations such as compass points and an appropriate inscription.
Update 23-SEP-09: Back in 1985, I was very deep into the trigonometry of sundial generation. Here are some notes I made for the purpose of explaining the analemic projections on the dials...
