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Eratosthenes JS Model Documents

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Main Document

Eratosthenes JS Model 

written by Todd Timberlake and Mario Belloni

The Eratosthenes JS 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 the relevant geometry.

The Eratosthenes 2D JS Model was developed using the Easy Java Simulations (EJS) version 5.  It is distributed as a ready-to-run html page and requires only a browser with JavaScript support.

Published March 8, 2014
Last Modified December 30, 2014

This file has previous versions.

Supplemental Documents

Eratosthenes Simulation EPUB 

An EPUB file containing the Eratosthenes simulation,
a general description, and the features of the simulation.

Published June 27, 2014
Last Modified June 27, 2014

This file is included in the full-text index.
This file has previous versions.

Source Code Documents

Eratosthenes JS Model Source Code 

This file contains the EjsS source code for the Eratosthenes JS Model.

Published April 8, 2014
Last Modified December 30, 2014

This file is included in the full-text index.
This file has previous versions.

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