Getting The Angles Right On A School Sundial


Early computer model for the sundial (left), and the completed design erected on the wall of the school building

For anyone who has ever enjoyed doing geometry at school, getting the angles right on a sundial may not sound so difficult. The sundial has to see the sun and the shadows have to tell the time. When sundial sculptor Tim Chalk was sketching out ideas for his latest work to erect a sundial at Dollar Academy, a leading Scottish school, he thought about the angles but decided to ask for help.

“This is more tricky than I have done before,” Tim explained. “The sundial will fit as a panel on the wall of one of the buildings, and this wall faces at an angle away from the south direction. I need to get the correct angle for the gnomon, and for all the hour lines, but then I need the equinox and the solstice lines as well. Please can you help me get these angles right?” Alastair Hunter worked with Tim to look at different possibilities. He produced computer models to show where the shadows would fall, and calculated the geometry and angles for a pleasing layout, which Tim could work from. The sundial is now in place and ready for its finishing touches.