Eratosthenes Model Documents This material has 2 associated
documents. Select a document title to view a document's
information. The Eratosthenes model displays the shadows cast by
two gnomons (sticks) at different locations on Earth. For one
gnomon, Sun is directly overhead (as would be the case if the
gnomon was on the Tropic of Cancer at the summer solstice). The
other gnomon is due north of the first gnomon. The sizes of the
gnomons are greatly exaggerated for visibility. This simulation
can be used to help illustrate how Eratosthenes was able to
measure the diameter of Earth using the shadows cast by two
gnomons, one situated due north of the other, on a day when the
southerly gnomon cast no shadow at all. The distance between the
two gnomons (along Earth's surface) can be adjusted. The length
of the shadow is given, and this length can be used to determine
the angle between the gnomon lines and from that the
circumference (and diameter, radius, etc) of Earth. Earth can be
hidden to give a better view of