METHODOLOGY

Hypothesis: Spiral galaxies are round disks and the apparent ellipse visible from earth is due to their orientation with respect to the observer.

Objectives

• Determine the expected distrubtion of apparent galactic rotation through computer simulation.
• Write a computer program to allow the apparent rotation of real and simulated galaxies to be determined.
• Identify galactic images from internet sources from which a random sample of galaxy images can be collected for analysis.
• Compare the simulated distribution of apparent rotation with that observed in the sample of real galaxy images to prove the hypothesis.

Assumptions

Tools for measuring apparent rotation

• A java application and applet was written that allows apparent rotation to be measured from images in GIF or JPEG formats. The applet is called the GalacticEllipseApplet and is available on this web server.
• In either of these tools, the user clicks and drags the mouse over a galaxy image to set the major axis of the apparent ellipse.
• The user moves a scrollbar to rotate a circle of appropriate radius about the major axis to determine the apparent rotation.
• The application version of the tool enables images to be directly loaded from any internet location
• The applet version of the tool restricts images to those stored on this web site. This is due to generic security restriction imposed by the Java programming language.
• The applet served by this web site uses simulated galaxy images only. Although real galaxy images could have been used by the applet, this would require these images to be mirrored on this site. This was not done in the final version of the Applet as it would be a potential violation of copyright. Those interested in using the application version of the applet to load galaxy images from the internet should contact the author.

Simulation

• A computer program was written using the OpenGL graphics language (Woo et al., 1997)
• One hundred cylinders were used to simulate the disks of spiral galaxies.
• These cylinders were randomly oriented to simulate the view from earth.
• A scatter plot was generated to verify that numbers were randomly generated and evenly distributed across the expected parameter space.
• The apparent rotation was measured using the application version of the GalacticEllipseApplet discussed above.
• Apparent rotation was grouped into bins of ten degrees and plotted.

Survey

• The internet was consulted to identify a suitable source of galaxy images, meeting the criteria outlined above.
• Apparent rotation was estimated and binned for each galaxy image
• Survey results were analyzed by comparing the distribution of apparent rotation in the real galaxy sample to the simulated galaxies from the computer simulation.