Instructions for Constructing a Celestial Sphere

For the dome, take an empty 2-liter bottle and, using the bottle’s label as a straight guide, cut off the top. Take a square piece of cardboard and draw a cross through the center and label the points N, E, S, and W. Tape the dome onto the cardboard so that it is centered over the cross. For more accurate data, tape a magnetic compass onto the northeast corner. Be sure that the north-south lines of both the compass and the board are parallel.

Now, take your celestial sphere model outside and put it in a place that stays sunny most of the day. Position it so that the board (or compass) points north. (Mark your location so you can put your model back if it gets moved.)

Take a marker and hold it over the dome. The marker’s tip will cast a shadow, and this shadow must touch the center of the cross on the cardboard. When you have it line d up, mark a dot on the plastic dome and record the time above it.

Make a solar observation every hour or so for as much of the day as possible (weekends are good time to try this). Try to take 3 measurements before noon, 3 around noon, and 3 more after noon. What patterns do you find? Which direction is the Sun in the early morning, at noon, and in the evening?

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