Eratosthenes Model View two gnomons shadows with this simulation.
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Eratosthenes Model Tags

viewer view display Realtime Shadows raytrace soft shadows moon shadows shadows view simulation 3D view simulation view gnomons shadow gnomons shadow simulation simulate gnomons shadow

Eratosthenes Model Description

Eratosthenes Model is a handy, Java based simulation application specially designed to enable you to view the shadows cast by two gnomons 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 the relevant geometry.

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