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Computer Program Detail Page

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Shapley's Globular Clusters
written by Todd Timberlake
The EJS Shapley's Globular Clusters Model shows the distribution of globular clusters around the plane of the Milky Way as determined by Harlow Shapley in 1918.  The Space View frame shows a 3D view of the distribution of the clusters around the galactic plane, along with the location of the Sun and Shapley's location for the galactic center (as well as the boundary of what Shapley called the "Big Galaxy") as determined by the cluster distribution.  Globular clusters are shown in different colors depending on how their distances were determined: using Cepheid variables (red), brightest stars in the cluster (green), or apparent diameter of the cluster (blue).  Other windows show a plot of the cluster locations projected onto the galactic plane, a plot of the number of clusters versus galactic longitude (showing a peak toward Shapley's proposed galactic center), and a histogram of distances from the galactic plane (showing a dearth of clusters very close to the plane).

The simulation allows the viewer to adjust Shapley's distances to account for the effects of absorption.  Absorption by dust in the galactic plane caused the cluster stars to appear dimmer than they should be from distance alone.  This led Shapley to overestimate their distances, with larger errors for clusters near the galactic plane where absorption effects are greatest.  The simulation uses a model for absorption proposed by Joel Stebbins in 1933.  Stebbins assumed a thin (1 kpc thick), uniform absorbing layer along the galactic plane, with light passing perpendicularly through the plane being dimmed by 0.36 magnitudes.  A slider in the simulation allows the user to adjust the dimming produced by the absorbing layer from 0 (Shapley's assumed value) up to 0.36 (the value found by Stebbins).  The simulation will also display Stebbins' revised galactic center and boundary, which essentially matches the modern view of the Milky Way.

Please note that this resource requires at least version 1.5 of Java (JRE).
1 source code document is available
Subjects Levels Resource Types
- Astronomy Education
= Curricula
- Historical Astronomy
= History of Astronomy
- Milky Way
= Galactic Center
= Interstellar Medium
= Milky Way Structure
- Stars
= Star Clusters
- Lower Undergraduate
- High School
- Upper Undergraduate
- Instructional Material
= Interactive Simulation
Intended Users Formats Ratings
- Educators
- Learners
- General Publics
- application/java
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Access Rights:
Free access
This material is released under a GNU General Public License Version 3 license.
Rights Holder:
Todd Timberlake
Cepheid variable, Harlow Shapley, Joel Stebbins, Milky Way, absorption, galaxy, globular cluster, interstellar dust
Record Cloner:
Metadata instance created May 18, 2011 by Todd Timberlake
Record Updated:
November 11, 2021 by Lyle Barbato
Last Update
when Cataloged:
May 18, 2011
Other Collections:

ComPADRE is beta testing Citation Styles!

Record Link
AIP Format
T. Timberlake, Computer Program SHAPLEY'S GLOBULAR CLUSTERS, Version 1.0 (2011), WWW Document, (
T. Timberlake, Computer Program SHAPLEY'S GLOBULAR CLUSTERS, Version 1.0 (2011), <>.
APA Format
Timberlake, T. (2011). Shapley's Globular Clusters (Version 1.0) [Computer software]. Retrieved July 12, 2024, from
Chicago Format
Timberlake, Todd. "Shapley's Globular Clusters." Version 1.0. (accessed 12 July 2024).
MLA Format
Timberlake, Todd. Shapley's Globular Clusters. Vers. 1.0. Computer software. 2011. Java (JRE) 1.5. 12 July 2024 <>.
BibTeX Export Format
@misc{ Author = "Todd Timberlake", Title = {Shapley's Globular Clusters}, Month = {May}, Year = {2011} }
Refer Export Format

%A Todd Timberlake %T Shapley's Globular Clusters %D May 18, 2011 %U %O 1.0 %O application/java

EndNote Export Format

%0 Computer Program %A Timberlake, Todd %D May 18, 2011 %T Shapley's Globular Clusters %7 1.0 %8 May 18, 2011 %U

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Shapley's Globular Clusters:

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 Shapley's Globular Clusters.

relation by Wolfgang Christian

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