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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.
1 supplemental document is available
1 source code document is available
Subjects Levels Resource Types
Astronomy
- Astronomy Education
= Curricula
- Fundamentals
= Night Sky
- Historical Astronomy
= History of Astronomy
- Solar System
= Earth
General Physics
- Measurement/Units
- Lower Undergraduate
- High School
- Upper Undergraduate
- Instructional Material
= Interactive Simulation
Intended Users Formats Ratings
- Learners
- Educators
- application/javascript
- application/zip
- text/html
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Access Rights:
Free access
License:
This material is released under a Creative Commons Attribution-Noncommercial-No derivatives 3.0 license.
Rights Holder:
Todd Timberlake and Mario Belloni
Keywords:
Earth, EjsS, Open Source Physics, angle, gnomon, javascript, measure, shadow
Record Cloner:
Metadata instance created March 8, 2014 by Mario Belloni
Record Updated:
June 15, 2015 by Lyle Barbato
Last Update
when Cataloged:
March 8, 2014
ComPADRE is beta testing Citation Styles!

Record Link
AIP Format
T. Timberlake and M. Belloni, Computer Program ERATOSTHENES JS MODEL, Version 1.0 (2014), WWW Document, (https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13203&DocID=3748).
AJP/PRST-PER
T. Timberlake and M. Belloni, Computer Program ERATOSTHENES JS MODEL, Version 1.0 (2014), <https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13203&DocID=3748>.
APA Format
Timberlake, T., & Belloni, M. (2014). Eratosthenes JS Model (Version 1.0) [Computer software]. Retrieved December 13, 2017, from https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13203&DocID=3748
Chicago Format
Timberlake, Todd, and Mario Belloni. "Eratosthenes JS Model." Version 1.0. https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13203&DocID=3748 (accessed 13 December 2017).
MLA Format
Timberlake, Todd, and Mario Belloni. Eratosthenes JS Model. Vers. 1.0. Computer software. 2014. 13 Dec. 2017 <https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13203&DocID=3748>.
BibTeX Export Format
@misc{ Author = "Todd Timberlake and Mario Belloni", Title = {Eratosthenes JS Model}, Month = {March}, Year = {2014} }
Refer Export Format

%A Todd Timberlake
%A Mario Belloni
%T Eratosthenes JS Model
%D March 8, 2014
%U https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13203&DocID=3748
%O 1.0
%O application/javascript

EndNote Export Format

%0 Computer Program
%A Timberlake, Todd
%A Belloni, Mario
%D March 8, 2014
%T Eratosthenes JS Model
%7 1.0
%8 March 8, 2014
%U https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13203&DocID=3748


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Citation Source Information

The AIP Style presented is based on information from the AIP Style Manual.

The APA Style presented is based on information from APA Style.org: Electronic References.

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The MLA Style presented is based on information from the MLA FAQ.

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Eratosthenes JS Model:

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relation by Lyle Barbato

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