Paper Plate Education
Video Excerpts: Sub-Solar Cup
With the Sub-Solar Cup you position yourself on top of a globe. Cross-hairs on the cup indicate the location on the earth (called the sub-solar point) where the sun would be found directly overhead at that moment.
To use the cup you hold it over the globe so that the circle of sunlight is centered on the crosshairs... Here, on a mid-March morning, you see the sub-solar point just of the coast of Brazil, near the mouth of the Amazon River.
...So while you can record the suns changing position from day to day, you can also record its changing position from week to week, through the seasons.
After the vernal equinox, you find that the sun has moved north of the equator.
As a variation, you can use a simple piece of pipe with crosshairs. Imagine it to be a water well, and simulate the work of Eratosthenes, who allegedly used the observation that a well located on the Tropic of Cancer reflected the sun on the summer solstice-- the well cast no shadow. This well defined the northern limit of the suns path and led Eratosthenes to determine the circumference of the earth.
Note: See the Analemma activity to plot a figure-8 analemma on a globe using the Sub-Solar Cup.
Copyright ©2012 Chuck Bueter. All rights reserved.