Make Your Own Sundial!
First, download one of the PDF files listed below and print it out. (You'll need Adobe Reader to do this.)
Sundials need to be adjusted according to your approximate latitude how far you are north or south of the equator. If you dont know your latitude, you can find it on most maps, or at one of these websites:
Cut and fold the printout according to directions printed on it. You might want two copies so that you can work on one while reading the directions on the other. The only hard part is pushing the pencil point through the center of the small circle. It helps to twirl the pencil as you push.
When youre done, the pencil should be perpendicular to the sundials face (not to the base). If the pencil wants to topple over, try taping the whole thing to another piece of paper or (better) to a sheet of cardboard. Mounting the sundial on cardboard also makes it easier to carry around. Cereal boxes are a great source of free cardboard.
Point the pencil due north or south if you live in the Southern Hemisphere. You can use a compass or a map to determine the proper direction, or you can just orient the sundial so that it agrees with your watch. (Subtract one hour from the watch if youre on daylight-saving time.) Then watch the shadow on the sundial change as the Sun moves from east to west over the course of the day.
This design is called an equatorial sundial because the face with the numbers is parallel to Earths equator. Its easiest to use at midwinter and midsummer, and hardest near the equinoxes around March 20th and September 23rd.
How Equatorial Sundials Work
The horizontal sundial, with a readout face parallel to the ground, is the most common design the one thats often found in garden stores. Horizontal sundials are easy to use but tricky to design and build.
The model youve just built is called an equatorial sundial because its readout face is parallel to Earths equator. Conceptually, its the simplest design, but it suffers from one practical disadvantage. Depending on the season, the pencils shadow may fall either on the top or the bottom of the readout face. Because the face is made of translucent paper, its easy to see the shadow even when its on the underside. This would be extremely awkward if the face were made of metal.
To see how this sundial works, imagine first that you lived at the North or South Pole. In that case, a stick planted upright in the ground would form both a horizontal and an equatorial sundial the two designs being identical at those locations. During the spring and summer, the Sun would rotate a full 360° around you every day, staying the same height above the horizon all the time. The sticks shadow would behave exactly like the hour hand on a 24-hour clock, staying the same length all day long while rotating at a constant rate. During autumn and winter, the Sun would never rise, and your sundial would be useless. But you would be too cold to care.
Do you find that your sundial isnt as accurate as you would like? That may be partly due to construction problems. Paper isnt very rigid, and no matter how carefully you do the folds, the sundial wont hold its shape perfectly. But there are also some more fundamental reasons why sundials and clocks tell different time. For more information, see our article Time and the Amateur Astronomer.