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Galileo's Sunspots JS Model
written by Todd Timberlake
The Galileo Sunspots JS Model illustrates the motion and changes in appearance of sunspots as they move across the disk of the Sun. Galileo's observation of the changing appearance of sunspots around 1611 provided strong evidence that the spots were actually blemishes on the surface of the Sun, an idea that conflicted with the Aristotelean notion of the perfections of the heavens.

The simulation shows four randomly generated sunspots, and one sunspot that has a user-defined latitude (to allow the user to examine the behavior of sunspots at various latitudes).  As the spots move across the Sun their appearance changes due to foreshortening and a slight tilt as the spots approaches the limb (or edge) of the solar disk.  These effects come about because the Sun's surface is spherical, not flat.  So the sunspot changes its orientation relative to the viewer as it moves around on the Sun's surface.

Controls allow the user to set the obliquity of a line representing the Sun's equator.  The user can adjust the obliquity of this line until the sunspots all move parallel to the line.  In this case the obliquity of the line is the actual obliquity of the Sun.  In addition, the model displays the elapsed time (in days) so that the user can determine the rotational period of the Sun by measuring the time required for a sunspot to complete its motion around the Sun.  (Note that the period of a sunspots motion is latitude-dependent, as it is in the real Sun.)
1 source code document is available
Subjects Levels Resource Types
- Historical Astronomy
= History of Astronomy
- The Sun
= Magnetic Activity
= Space Weather
- Lower Undergraduate
- Middle School
- High School
- Instructional Material
= Interactive Simulation
Intended Users Formats Ratings
- Learners
- General Publics
- application/zip
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Access Rights:
Free access
This material is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license.
Rights Holder:
Todd Timberlake
EJS, EJsS, Galileo, OSP, obliquity, solar rotation, sunspot
Record Creator:
Metadata instance created December 31, 2014 by Todd Timberlake
Record Updated:
June 15, 2015 by Lyle Barbato
Last Update
when Cataloged:
December 31, 2014
ComPADRE is beta testing Citation Styles!

Record Link
AIP Format
T. Timberlake, Computer Program GALILEO'S SUNSPOTS JS MODEL, Version 1.0 (2014), WWW Document, (https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13395&DocID=3979).
T. Timberlake, Computer Program GALILEO'S SUNSPOTS JS MODEL, Version 1.0 (2014), <https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13395&DocID=3979>.
APA Format
Timberlake, T. (2014). Galileo's Sunspots JS Model (Version 1.0) [Computer software]. Retrieved June 16, 2024, from https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13395&DocID=3979
Chicago Format
Timberlake, Todd. "Galileo's Sunspots JS Model." Version 1.0. https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13395&DocID=3979 (accessed 16 June 2024).
MLA Format
Timberlake, Todd. Galileo's Sunspots JS Model. Vers. 1.0. Computer software. 2014. 16 June 2024 <https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13395&DocID=3979>.
BibTeX Export Format
@misc{ Author = "Todd Timberlake", Title = {Galileo's Sunspots JS Model}, Month = {December}, Year = {2014} }
Refer Export Format

%A Todd Timberlake %T Galileo's Sunspots JS Model %D December 31, 2014 %U https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13395&DocID=3979 %O 1.0 %O application/zip

EndNote Export Format

%0 Computer Program %A Timberlake, Todd %D December 31, 2014 %T Galileo's Sunspots JS Model %7 1.0 %8 December 31, 2014 %U https://www.compadre.org/Repository/document/ServeFile.cfm?ID=13395&DocID=3979

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Galileo's Sunspots JS Model:

Is Version Of Galileo Sunspots

The Galileo's Sunspots JS Model is a Javascript version of the Galileo Sunspots EJS Model.

relation by Todd Timberlake
Is Based On Easy Java Simulations Modeling and Authoring Tool

Use the Easy Java Simulations Modeling and Authoring Tool to edit and to explore the source code for the Galileo's Sunspots JS Model.

relation by Lyle Barbato

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