Shadows on the Equinox
at Charleston Middle School

 

On September 21, 2001, eighth grade students at Charleston Middle School in Charleston, Illinois measured the shadow cast by a vertical meter stick on the day before the autumnal equinox. They worked in teams and attempted to determine the shortest shadow cast during each class period. They then recorded the times and calculated the angles of the shadows. Their data is shown below.

In addition to measuring shadows, the students also examined sunspots through an 8 inch Meade Dobsonian telescope using a special solar filter designed for safe viewing.

Period

Time

Shadow Length (cm)

Shadow Angle (degrees)

Core A

9:50

148

56

Core B

10:30

117

49.5

4th

11:20

94

43.2

5th

12:00

84

40.0

Lunch

12:30

81

39.0

Core C

12:50

79

38.3

Core D

1:30

83

39.7

Core E

2:15

94

43.2

Float

2:45

113

48.5
Discussion Questions

* Why did the Sun appear to be at its highest midday point at 12:50 pm rather than at noon?

* Over what degree of N-S latitude is the Sun on the equinox?

* What is the significance of the calculated shadow angle at "solar noon" on the equinox?

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