The simplest sundial is a vertical stick rising from a flat horizontal surface. As the Sun rises, passes the highest point in its path (at noon and to the south, in the northern hemisphere) and sets, the shadow rotates around the stick in a clockwise direction, and its position can be used to mark time. Indeed, it has been claimed that the “clockwise” direction in which the hands on a clock rotate was chosen for this reason.
“Some people can tell what time it is by looking at the sun. But I have never been able to make out the numbers!” — Attributed to an essay by a student in elementary school.
A sundial with a vertical pointer (“gnomon”) will indicate noon correctly when its shadow points north. However, such a sundial will work at all times if the pointer is slanted, to point towards the pole of the celestial sphere (towards the Pole Star). The angle between it and the base then equals the geographic latitude of the user. Ornamental sundials are often found in parks and gardens, with the pointer widened into a triangular fin, which must point northwards.
A sundial of this type can be constructed from folded cardboard or stiff paper: click here to see the basic design, which can be printed and then photocopied onto suitable sheets of stiff paper or cardboard (you may want to use the “option” menu to reduce size to 90% before printing – but make sure to return the setting to 100% afterwards!). It is meant to be used at a latitude of 51 degrees – Bromley and Orpington.
Part 1 – The Gnomon
- Print out the design onto white paper or stiff card if your printer has the capability.
- Cut the paper in two along the cut line “a” to “b”.
- On the “gnomon” piece cut along both “c” to “d” and “e” to “f” right from one edge of the paper to the other. Also cut the short line from “g” to “h” (also from the edge of paper.
- Now score and fold along the thin grey fold lines. Do not worry if you fold right along the lines and beyond to the edge of the paper – this is fine! First, turn the paper over so you cannot see the printed side – now fold in half along the centre of The Gnomon. Turn the paper back the right way up and fold (along the fold lines) each of the two outer “flaps” of paper towards The Gnomon.
- With The Gnomon folded, carefully hold together its two halves and cut along the curved line “i” to “j” with a pair of scissors. Now you will see that the line “g” to “h” and the “gnomon” are all one cut.
- Using the already made folds, bring the two halves of The Gnomon together while passing the “AA” flap over the “BB” flap – they should lightly lock together. You should now have a flat piece of paper with a gnomon standing up off your work surface.
Part 2 – The Dial
- Now using the “dial” piece of paper, cut along line “k” to “l” but NO FURTHER.
- Take the “gnomon” piece and slide the “gnomon” into the cut line “k” to “j” on the “dial” piece. The point “i” on the “gnomon” piece should snugly line up with the “k” cut on the “dial” piece. Slide the outer flaps of the “gnomon” piece under the “dial” piece.
A sunny day is best for positioning you sundial. Make sure you keep The Gnomon upright. Remember at 12 o’clock (noon) GMT in Bromley or Orpington the Sun lies due south so it is easy to set up the dial on a flat surface. But at other times as long as it is sunny you can align the dial using your watch although depending on the time of year the time can be about a quarter of an hour out.