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Gnomon Model
written by Todd Timberlake
The EJS Gnomon model simulates the shadow cast by a gnomon (the part of a sundial that casts the shadow) over the course of a day for any day of the year and any latitude on Earth. The program gives you the option to use mean Sun (which moves relative to the stars at a constant rate throughout the year) or true Sun (which varies its apparent speed relative to the background stars). The default is to use true Sun. The program also shows the observer's horizon plane on the spherical Earth, as well as the ecliptic and the apparent path of Sun. The Earth View can be set to let Earth rotate or remain fixed

EJS Gnomon model was created using the Easy Java Simulations  (Ejs) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.   Double clicking the ejs_astronomy_Gnomon.jar file will run the program if  Java is installed.  Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models.  Additional Ejs models for astronomy are available.  They can be found by searching ComPADRE for  Open Source Physics, OSP, or Ejs.

Please note that this resource requires at least version 1.5 of Java (JRE).
2 supplemental documents are available
1 source code document is available
Subjects Levels Resource Types
- Astronomy Education
= Curricula
- Historical Astronomy
= History of Astronomy
- Lower Undergraduate
- Middle School
- High School
- Instructional Material
= Interactive Simulation
Intended Users Formats Ratings
- Educators
- Learners
- General Publics
- application/java
  • Currently 5.0/5

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Access Rights:
Free access
This material is released under a Creative Commons Attribution 3.0 license.
Rights Holder:
Todd Timberlake
EJS, Earth, Easy Java Simulations, OSP, Open Source Physics, Sun, gnomon, shadow
Record Cloner:
Metadata instance created August 18, 2009 by Mario Belloni
Record Updated:
June 6, 2014 by Andreu Glasmann
Last Update
when Cataloged:
August 18, 2009
Other Collections:

ComPADRE is beta testing Citation Styles!

Record Link
AIP Format
T. Timberlake, Computer Program GNOMON MODEL, Version 1.0 (2009), WWW Document, (
T. Timberlake, Computer Program GNOMON MODEL, Version 1.0 (2009), <>.
APA Format
Timberlake, T. (2009). Gnomon Model (Version 1.0) [Computer software]. Retrieved May 28, 2017, from
Chicago Format
Timberlake, Todd. "Gnomon Model." Version 1.0. (accessed 28 May 2017).
MLA Format
Timberlake, Todd. Gnomon Model. Vers. 1.0. Computer software. 2009. Java (JRE) 1.5. 28 May 2017 <>.
BibTeX Export Format
@misc{ Author = "Todd Timberlake", Title = {Gnomon Model}, Month = {August}, Year = {2009} }
Refer Export Format

%A Todd Timberlake
%T Gnomon Model
%D August 18, 2009
%O 1.0
%O application/java

EndNote Export Format

%0 Computer Program
%A Timberlake, Todd
%D August 18, 2009
%T Gnomon Model
%7 1.0
%8 August 18, 2009

Disclaimer: ComPADRE offers citation styles as a guide only. We cannot offer interpretations about citations as this is an automated procedure. Please refer to the style manuals in the Citation Source Information area for clarifications.

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 Electronic References.

The Chicago Style presented is based on information from Examples of Chicago-Style Documentation.

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Gnomon Model:

Is Based On Easy Java Simulations Modeling and Authoring Tool

The Easy Java Simulations Modeling and Authoring Tool is needed to explore the computational model used in the EJS Gnomon Model.

relation by Mario Belloni
Covers the Same Topic As Eratosthenes Model

The Eratosthenes model displays the shadows cast by two gnomons (sticks) at different locations on Earth. 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.

relation by Mario Belloni

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