GalaxSee

Test Case(s): I was able to prove the GalaxSee valid based on the rotation of the Earth and the Sun. The concept is physically fundamental. Any valid galactic simulation tool should be able to simulate the movement of the Earth about the Sun. By discovering through trial and error which value of tangential velocity would create a stable rotation, and then comparing that experimental value to the actual accepted value of .01719 AU/day I was able to find that the experimental value was reasonably close to the accepted value. In addition when the accepted value is filled in the proper field, the orbit is perfectly stable and constantly repetitive. In addition I ran a test involving the creation of a random galaxy and the total energy only varied slightly. This program can also be proven by the Virial theorem because when the galaxy is stable there is a 2:1 ratio between potential and kinetic energy. When it comes to validation I would say that this tool is perfectly valid, and can be used with little to no error assured. In addition when the model for Mac was ran against the model for Windows, the model results were practically identical, after the shield modification discrepancy was taken into account. This proves that if the model is valid on Windows, which is the program it was initially tested on, it will also be valid on Mac, thereby completely validating the model.

I would recommend this program for high school students in such classes as astronomy or advanced physics. This program could be used as a visual aid for lower leveled science, however I believe that in order to actually comprehend this program, students should have some background in the forces at work. A general physics course wouldn't really delve into astrophysics as much as a higher level physics course such as AP Physics. This program is perfect for mid year astronomy students though. I believe that this program meets the NSES science and technology content standard E, and will facilitate further the development of content standard D by allowing students to see how the galaxy's in the universe came to be what we know them to be. And NJSES standards 5.7 A and B and 5.9 A,B,C, and D.

Documentation Review: For the Macintosh program, the software downloaded and opened properly. There were some minor difficulties in that the software opened without any default galaxy file, and some instruction on how to start a new model would have been useful. Editing the galaxy was difficult due to the need to restart the galaxy after any change. It is difficult to distinguish individual stars when the trace option is activated. A possible solution to this would be to give the user an option to change the color of the trace from the stars, so instead of having to distinguish individual red stars on a red background, it might be a possibility to allow for red stars with a green trace so the current position of the stars can be separated from the past position of the stars. Although I find the help menu helpful for the over all program, it is lacking in a few minor areas such as: Additional options of "View" (tails, red shift, depth cueing, ect.), and "Action" (mainly wobble and rotate z axis). I also found the help balloon action less then helpful. It appeared that for everything I wanted help on there wasn't a help balloon, and for everything I didn't need help on the were several help balloons. Over all I would say this is a good tool, but if I had the option I would recommend the windows version instead, however there are some things I believe that can be changed about the windows version as well. For the windows version, it was difficult to determine the proper download link for the software. Currently the download link is far down on the page, below page graphics, and it is necessary to scroll down to find the link. I found that the online help menu is actually customized for the power Mac program, however the help document that comes with the software is set up for both Mac and PC. This is only minor since the only difference is in the fact that the online help menu refers to the step-by-step setup as "down load the software onto you Power Mac." The help menu available through the actual GalaxSee program needs a lot of work. I suggest you make the tutorial available through the help menu since that is where I would expect to find it. The tutorial is much better than the Mac version, however it also doesn't address the "View" options. For each integration method, the default timesteps for default models resulted in little problems with conserving energy and momentum. Decreasing the timestep did not result in substantial changes in the result, whereas an increased timestep did cause error to occur. This is to be expected with models that use explicit integration methods. Problem(s) annotations: I at first had trouble opening a new galaxy. I also initially had trouble seeing the galaxy. Some of the options were not explained well as noted above. Recommendations: The help document should be improved, but other then that, it is perfect.