|
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.
 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.
 Using
an opaque plastic cup, on the bottom, dead center, drill a small hole.
On the side, cut out a large viewing port...
 ...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.
 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.
 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.
 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.
 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.
 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.
 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.
| 
