Notes on sundials: where the hour lines go, how to find north, and why the shadow and the clock rarely agree.
- 01Noon marks and meridian lines
A line on the floor that the sun crosses at the same moment every day, and the giant versions built into churches.
- 02Finding true north with a stick
A vertical stick, a loop of string and two marks in the dust give a north–south line good enough to set a dial.
- 03Why the style points at the pole
The edge that casts the shadow is parallel to the earth's axis, so on a flat dial it rises at the angle of the latitude.
- 04Hour lines on a horizontal dial
On a flat dial the hours are not 15° apart. One line of trigonometry says where they go.
- 05Why the sundial and the clock disagree
Sundial time runs up to sixteen minutes ahead of the clock and fourteen behind. Two causes, one curve.
- 06The figure of eight
Plot the sun's declination against the equation of time and you get the analemma, lopsided for a reason.
- 07Vertical dials on a south wall
The commonest dial in Britain is painted on a wall. Its style points down, and its hours run the other way round.