How to Use the Sun to Determine Latitude

Rest a drinking straw along the base of the protractor so that it is exactly parallel to the line that runs between the 0 and 180 degree markers. Tape the straw into place. Use multiple pieces of tape so that the straw does not move.

Thread one end of the string through the hole in the protractor and tie it in a knot. Thread the other end of the string through the hole in the nut or washer and tie this off as well, creating a plumb bob that permits the protractor to be used as an inclinometer.

Wait until the sun is at its highest point in the sky. Turn to face the sun, holding the protractor base side up (that is, with the straw on top) and exactly perpendicular to the ground --- you'll know when it's perpendicular because the string will be flush with the flat side of the protractor, not hanging off to one side.

Hold the index card behind the protractor and slowly raise the protractor up towards the sun. Do not look directly at the sun through the straw. Observe the index card instead. When it is sighted directly at the sun, you will see a bright point of light projected through the straw and onto the card.

Note the marked angle where the string crosses the protractor. This is the zenith angle of the sun, and is complementary to the sun's angle of elevation --- if the sun is 70 degrees in altitude, the protractor will record the zenith angle of 20 degrees.

Refer to the solar declination table and find the declination for the current date. Add the declination to the zenith distance to get your latitude in degrees.