To construct a permanent compass rose and use it to find directions
About 60 minutes, including the time between 11:30 A.M. and 12:30 P.M. standard time (add 1 hour for daylight savings time).
- Move the class outdoors to a sunny spot. If possible construct this compass rose on a hard surface where it can be marked in place permanently. As in the previous exercise, lay out a 60-cm circle and place the gnomon in the exact center. Every 5 minutes between 11:30 A.M. and 12:30 P.M. standard time mark the points at which the moving shadow of the gnomon intersects the circle and mark the end of the shadow.
Figure 2. Creating a compass rose.
- Label the point at which the shortest shadow intersects the circle "N" for north. This point may not be reached at exactly 12:00 noon standard time. For one thing, solar time is exactly standard time at only one meridian in each time zone, and other factors cause solar time to deviate from clock time.
- Remove the gnomon from the circle. With a meterstick, draw a straight line connecting the "N" point, the center point of the circle, and the point opposite the "N" point on the circle. Label this opposite point "S" for south.
- If available, use a wooden compass with chalk (the kind used to draw geometric constructions on the chalkboard) to bisect the right-hand arc between N and S to locate east. Label the point "E." Bisect the opposite arc to locate west and label that "W." Continue bisecting arcs until at least eight points of the compass have been marked (see figure 2).
Back in the classroom, discuss the fact that the students have found the compass points on their playground by using the Sun's shadow. Be sure that they understand that when they stand facing north as they have marked it, they are actually looking north. How do they know this? When the Sun's shadow is shortest it is solar noon, the Sun is directly south, and its shadow will point north. Have the students record in their journals information about this activity.
Refer the students to maps to study compass rose designs. Why is the compass rose on a map important? (It tells us which way is north on that map.) If they want to, students can decorate their permanent compass rose to match one of the examples they find.
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