Paper Plate Education
"Serving the Universe on a Paper Plate"

Activity: Gno Problem Mon

The following text is reprinted from GLPA Proceedings, 1993, p. 35. It was written by Jeanne Bishop as part of a series of in-planetarium lesson plans. Used with permission.

5. SUNDIAL: Foam plate, scissors, printed circular protractor (angles of azimuth are measured), tape nail, plastic straw, marker, a very bright light (I clamped one to a ringstand on a cart and wheeled across one end of the room). Cut out the "angle dial." Tape it to the bottom of the foam plate (dial is elevated). Punch a hole at the center of the dial. Wiggle the nail to make the hole just large enough to hold a straw. Mark the straw upright. Mark north where the 0 is on the dial. Mark east where 90 is on the dial. Mark south where 180 is on the dial. Mark west where 270 is on the dial. ''When I turn on this light, my pretend-sun, do you think you will see a shadow? If I keep the "sun" here, how could a shadow fall across my dial? (Student answers) Turn on the light and note how the shadows point away from it. Move the light-sun across an arc at the south end of the room, changing its height to greater angles by sliding the light higher on the ringstand. Students watch what happens to the direction and height of their shadows. Write the name "Gnomon" on the board and define it. Discuss sundials the students may have seen. (Some realized that the gnomon was tipped and I invited them to tip their straws in the north direction. I moved the light-sun through the same arc.) Straws may be reinforced with tape. "Take your dial home and watch how the shadow changes with the real sun in the day. Put it in the same spot each time you use it, and face it in the correct earth directions. If you use it now and then again in December, do you think the directions of the shadows at sunrise and sunset will be the same? Do you think the length of the gnomon shadow will be the same? Try it!"

Contributed by Jeanne Bishop.

GLPA Proceedings, "Sundial", 1993, p. 35.

Also see GLPA Proceedings, 1992, p. 81, by Wayne James.

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