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Lab #27.8
Light: Sunballs
Purpose
In this activity,
students will estimate the
diameter of the sun.
Discussion
Take notice
of the round spots of light
on the shady ground beneath
trees. These are sunballs—images
of the sun. They are cast by
openings between leaves in
the trees that act as
pinholes. The diameter of a
sunball depends on its
distance from the small
opening that produces it.
Large sunballs, several
centimeters or so in
diameter, are cast by
openings that are relatively
high above the ground, while
small ones are produced by
closer “pinholes.” The
interesting point is that
the ratio of the diameter of
the sunball to its distance
from the pinhole is the same
as the ratio of the sun’s
diameter to its distance
from the pinhole.
Knowing that
the sun is approximately
150,000,000 km from the
pinhole, careful measurement
of this ratio tells us the
diameter of the sun. That’s
what this experiment is all
about. Instead of finding
sunballs under the canopy of
trees, you’ll make your own
easier-to-measure sunballs.
Required Equipment
Small piece of
cardboard, meter stick
Download
Student Worksheet
Teacher Notes
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