Sundials have been used for centuries to determine the time of day using the sun's shadow. There are many different methods and techniques for building sundials; aside from some math work, most of the designs are relatively easy to build. The easiest sundial is a stick rising from a flat horizontal surface, or a stick in the ground. As the sun rises throughout the day, the stick's shadow will rotate clockwise around the stick and can be used to tell time. Other designs are slightly more difficult to make.
To make this sundial design, you will need a piece of cardboard about 10 inches long, a drinking straw and a protractor. The sundial uses specific measurements drawn on the cardboard to determine the time. Place the straw through the centre of the cardboard with a circle drawn around the centre. Determine the length of the bottom end by multiplying 10 by the cotangent of latitude. The sundial is set up like the earth in that the shadow of the straw will rotate 360 degrees around the straw as the earth moves around the sun.
To make a horizontal sundial, you must first mark the hour angles. Draw one baseline. Write 6 a.m. and 6 p.m. opposite each other on each end of the line. Draw a perpendicular line for the 12 o'clock hour. There are math formulas for figuring out all of the specific hours throughout the day, but they are complicated. Estimate to find the approximate time of day. The formula for figuring the accurate time is tan D= (tan t) (sin 0). D represents the angle the hour line makes with the noon line, the t is the time measured from noon in degrees and minutes of arc and the 0 represents the latitude of the position of the sundial.
This sundial activity is geared for beginners and younger students looking to learn about the sundial's importance. Remind the students how slowly the sun seems to move through the sky during the day. For best results, stand in a position where you can see the sun with an unobstructed view. The late morning to early afternoon hours work well. If the students stand in the same location, they can use different landmarks, such as a tree, car and a flag pole to mark certain times of the day. The students become part of the sundial and will learn how sundials work to tell time.
Create a sundial designed to use indoors with a piece of cardboard with a circle drawn on it. Place a straw in the centre of the circle, through the cardboard. Decorate the sundial however you choose. Draw two similar rectangle triangles, which need to be proportionally measured to the sundial design, with one angle exactly similar to the line of latitude where the sundial is positioned. Place the triangles on the bottom side of the sundial. Lean the straw so the lower part fits in with the paper. Place the sundial where it can get sun and use a compass to draw the correct coordinates on the sundial. Point the end of the straw to the North.