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Paper Plate Education
"Serving the Universe on a Paper Plate"

Video Excerpts: Sub-Solar Cup 

The following pictures and narration are excerpted from the Paper Plate Astronomy  video.

dsc00002.jpg (32385 bytes)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.

dsc00003.jpg (12920 bytes)Using an opaque plastic cup, on the bottom, dead center, drill a small hole.  

dsc00004.jpg (12838 bytes) On the side, cut out a large viewing port...

  dsc00005.jpg (9664 bytes)...and on the front affix these crosshairs, again so they cross dead center. 

On a sunny day, align your globe north and south.  Your meridian and the globe’s lines of longitude should be parallel.  

dsc00007.jpg (28986 bytes)Concurrently position it so your location is on the top of the globe.  In this example we are filming from Cleveland, Ohio, so a figure placed on Cleveland would be upright.  

dsc00008.jpg (28470 bytes)To help align the globe accurately, place a bubble level on top--in this case, Cleveland--and adjust it, still keeping the globe aligned north and south. 

dsc00009.jpg (15166 bytes)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.

dsc00010.jpg (22861 bytes)Later in the morning you can see how the path of the sun has shifted westward into the interior of Brazil.  This introduces other lessons in geography.

dsc00011.jpg (21509 bytes)Later this mid-March afternoon, you see the sun has moved over the Pacific Ocean, but still just below the equator.

...So while you can record the sun’s 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.

dsc00012.jpg (23700 bytes)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 sun’s 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.

 

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Copyright 2012 Chuck Bueter.  All rights reserved.