Sun Tracker by A. Cool


* sturdy cardboard, large if possible
* large/wide straw (e.g., type used for smoothies)
* two thin nails (with heads), about 1 inch long
* thumb tack and string for drawing large circles

* scissors or box cutter
* pencil and markers
* rubber eraser or large paper clip (optional)
* stone or other weights (optional)

1. Compass rose: a base for the Sun tracker

A "compass rose" showing all the cardinal directions (north, south, east, west, etc) can be made from some stiff cardboard, e.g., from a sturdy box). Ideally the cardboard should be large enough to cut out about a 20 inch diameter circle. Somewhat smaller should be okay, too. Put a tack in the middle of the piece of cardboard and tie the string to it. Attach the string to a pencil and trace out a large circle. Cut out the circle and then draw a series of lines radiating from the tack hole to mark the cardinal directions (N, NE, E, SE, S, SW, W, NE). The kids can decide if they want to add in-between directions as well: NNE, ENE, ESE, SSE, SSW, WSW, ENE, NNE. Care should be taken to place the radiating lines at appropriate angles relative to one another. There are many different ways this could be done. A protractor could be used but is not necessary. There are fun ways to do it using a drafting compass. A ruler could also be used to good effect. Probably the kids can figure it out. The compass roses can be made much more beautiful (as they have been historically). Here are some examples from a google search on "compass rose." compass_rose1 compass_rose2 compass_rose3 compass_rose4 compass_rose5 NOTE: A magnetic compass will be needed to orient the compass rose correctly when you go outside. Once it's correctly oriented, you may want to put some rocks or other weights on it to hold it in place while the device on top (see below) is moved around.

2. Finding the direction to the Sun

A second piece of cardboard can be used to determine the cardinal direction of the Sun. This can be made from a semi-circle of cardboard that is about the same diameter as the compass rose. Draw a line that marks the diameter of the circle. Then place a tack in the middle and use the string to trace out a circle. IMPORTANT: Add an extra 1 to 2 inches to the bottom of the semi-circle before you cut it out(see first image above). To support the semi-circle and make it stand up straight, you can use two small rectangles of cardboard with slots cut in them. Place one near each end of the semicircle to stand it up (see second image above). Now you can measure the direction to the Sun! The kids can figure out how. (One important detail is that the shadow of the semi-circle needs to cross the tack hole at the center of the compass rose--see third image above. The kids will probably figure that out, too.)

3. Finding the height ("altitude") of the Sun

A straw can be used to measure the Sun's altitude once the direction has been found. A large stiff straw of the sort used for smoothies works well. Put a small nail through the straw close to one end (e.g., 1 inch). Then attach it to the cardboard semi-circle at the position of the tack hole that was used to draw the semi-circle (see images above). To help hold it in place, a rubber eraser or metal binder clip may help. The kids can figure out how to use the straw to point at the Sun. WARNING: they may be tempted to try to look through the straw at the Sun, which is not a good idea! Instead, they should experiment with rotating the straw up and down until it produces the minimum possible shadow. When the shadow is as small as possible they will see a circle projected onto the cardboard compass rose below--with the nail through its center--see image above at right.) NOTE: it can be hard to see what's going on with the straw's shadow when holding the straw with a hand. A better way is to add a tiny thin "handle" to the other end of the straw in the form of a nail. A a 1 inch nail works well. Attach it to the other end of the straw so it sticks out of the straw and away from the cardboard semi-circle. Then by holding onto this nail, the kids can move the straw up and down without the shadow of their hand getting in the way. The kids can decide how they want to record how high the Sun was at a given time on a given day, e.g., using pencil markings on the cardboard. Or they can use a protractor to mark angles along the edge of the semi-circle and then record the numbers each time they make a measurement. The reading for the images above was done around noon, when the Sun was due south and as high as it would get that day. The reading below was made a few hours later when the Sun had moved into the southwest and was on its way down. (Note that for purposes of taking these pictures, the nail at the upper end of the straw was used to keep the straw in place on the cardboard. This won't be necessary in general.)