Run 2 simulations which differ ONLY in one control setting. You may choose any of the controls listed above EXCEPT the number of stars. This only affects the quality of the simulation: using more stars looks better, but takes longer to run. For example, you might investigate what happens when you change the mass, or the distance of closest approach.

Record and report the control settings which you use. Which control did you change? From what to what? Describe the results of your simulations. How did things change when you altered the control setting?

• a) Judging from the size of the bulge and the shape of the spiral arms, is this likely to be classified as an Sa or an Sc galaxy? Briefly describe why.
• b) The color of this galaxy changes gradually from red to blue as one moves outward from the center. Given what you know about the evolution of stars, what does this color gradient imply about the average ages of stars at different radii?
• c) Stars form together in clumps. Do you see any evidence for recent star formation in this image? Where?