APS Excellence in Physics Education Award
November 2019

Education Prize Logo
Science SPORE Prize
November 2011

NSF Logo
The Open Source Physics Project is supported by NSF DUE-0442581.

Galileo's Sunspots JS Model Documents

This material has 2 associated documents. Select a document title to view a document's information.

Main Document

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.)

Published December 31, 2014
Last Modified December 31, 2014

Source Code Documents

Galileo's Sunspots Source Code 

This source code zip archive contains an XML representation of the Galileo's Sunspots JavaScript Model.   Unzip this archive in your EJS workspace to compile and run this model using EjsS ver 5.1.  Although EjsS is a Java program, it creates a platform independent stand-alone JavaScript program that runs on most browsers from this source code.

Last Modified December 31, 2014

OSP Projects:
Open Source Physics - EJS Modeling
Physlet Physics
Physlet Quantum Physics
STP Book