Raymond W. Brooks
Purpose: To provide an activity for a Science Fair Project distinguishing Solar Noon from
Clock Noon.
Objective: Upon completion of this investigation, the student will be able to use a
gnomon record to explain the difference between Solar Noon and Clock Noon
for their longitude.
Materials: Gnomon and gnomon board, Plain white paper (8 ½" X 11"), magnetic
compass, ruler, masking tape, watch or clock, drafting compass
Procedure:
1. At the middle of the long side of the paper, measure in about 2 ½ inches and make a small hole for the gnomon.
2. Place the gnomon through the hole and tape the paper to the board. (I found using a paper clip and bending a part of it straight up for the gnomon worked very well.)
3. Write your name and date in the lower right hand corner of the paper.
4. Place your gnomon outdoors where sunlight will not be interfered with for your observation period.
5. Make sure the gnomon is level and using your magnetic compass, draw a line showing the direction for magnetic north.
6. Make a small dot at the end of the gnomon shadow line every 15 minutes between the hours of 10:00 A. M. and 2:00 P.M.
7. Using a Plastic ruler, connect the dots using a smooth curved line.
8. Using your drafting compass, place the pivot point in the gnomon hole.
9. Open the compass so that it will cross the shadow line at two points.
10. Make an arc on each side of the shadow line.
11. Open your compass so that is a little more than half way between the twoarcs.
12. From each arc on the shadow line, place the pivot point of the compass and construct two new arcs that will intersect each other.
13. Using your ruler, draw a straight line from the gnomon hole to the place where the two arcs intersect.
Observations: The straight line representing Solar Noon did not cross the shadow line at Clock Noon.
Conclusion: Places with different longitudes will have a different Solar Noon even though their Clock Noon is the same.
