This program creates a simulation of what happens when two galaxies interact. Using force equations leap-frogged for time, this program is amazingly realistic in its display. The program creates two views: a x-y view and a x-z view. These angles show the galaxies from a top perspective and an edge-on perspective. The code for this program is based upon BASIC code presented in the December 1988 issue of Astronomy Magazine. The original BASIC code was created and copyrighted by M.C. Schroeder and Neil F. Comins. This program is not an update to a previously released program called Galaxy Collisions-3D, although both programs were inspired by the same article.
Inputs
The program requests the following information:
Target Galaxy Rings: This is how many rings the target galaxy has.
Target Galaxy Stars/Ring: This is how many stars are on each ring. You cannot have different amounts per ring. The maximum number of stars is 2000, so plan accordingly. The program will re-set the setting to the default if you go over the amount.
Intruder Galaxy Mass %: This is the size of the intruding galaxy in terms of percent size of the target. There is no limit to the mass size, although it must be larger than 0.01% of the Target galaxy. You cannot alter the mass of the Target.
Coordinates X, Y, Z: This is the positioning of the Intruder galaxy in relation to the Target.
Velocity X, Y, Z: This is the velocity of the Intruder galaxy at a moment when theoretically no gravity interference has occured already (ala Star Trek).
Steps: The number of time steps to run the simulation.
Limitations
Galactic Interaction can only have up to 2000 total stars divided up into a maximum of 30 rings. This was done to minimize resource impact. If there is sufficient desire, I can widen these limits to over 30,000 stars easily. However, the memory required would be increased dramatically.
System Requirements
Galactic Interaction requires a 68020 or better processor and System 7.x only. It also prefers the thread manager. Only when the thread manager is loaded can you end a simulation while it is being displayed. If you do not have the thread manager, you cannot resume use of your mac until the simulation ends. The thread manager is built into System 7.5 and is an extension available from Apple for Macs running System 7.1.x.
Troubleshooting
Memory Messages:
Because the program uses memory buffers related to the size of the window, as you increase the size of the window, the memory demand increases. At one point, you may get a message asking for more memory. Whatever number the box tells you, simply add it to the current memory amount allocated to the program. To do this, click on the program icon, choose "Get Info…" from the "File" menu. In the box that says "Preferred," add that number and the one you wrote down into the box. Then re-launch the program. Now you can resize to that same size without having the message.
Resizing:
The window is resizeable ONLY when a simulation is not running. The window is resizeable using the standard grow box (it is not displayed on the window, but click in the lower right anyway to drag it) and the zoom box.
Stopping a Simulation:
When you have the thread manager installed (See System Requirements section), you can stop a simulation at any time by pressing Command+G.
Saving Simulations:
You can also save settings for future retrieval in case you found a simulation stimulating. At some point, I may add in the ability to save the simulation as a QuickTime movie. That would be far off into the future.
Any distribution must include this "READ ME!" file and the "Galactic Interaction" program. This file cannot be sold for profit individually or collectively without the express, written consent of the author, Neil Schulman. There are no exceptions. This file may be distributed by any online service that does not attempt to sell this file individually or collectively with other programs. This file may be included on any BBS system or internet archive site under the same terms as commercial services. This file may be included on the Pacific Hi-Tech CD-ROMs of internet posted shareware/freeware programs. This file may be included on any Macintosh User Group disk set, but CD-ROM producers must send notice before placing this program on the CD-ROM.
All trademarks used are properties of their respective owners and are used for informational purposes only.
Neil Schulman hereby disclaims all warranties relating to this software, whether express or implied, including without limitation any implied warranties of merchantability or fitness for a particular purpose. Neil Schulman will not be liable for any special, incidental, consequential, indirect or similar damages due to loss of data or any other reason, even if Neil Schulman or an agent of his has been advised of the possibility of such damages. In no event shall Neil Schulman be liable for any damages, regardless of the form of the claim. The person using the software bears all risk as to the quality and performance of the software.
US Governement:
Government End Users: If you are acquiring the Software and fonts on behalf of any unit or agency of the United States Government, the following provisions apply. The Government agrees:
(i) if the Software and fonts are supplied to the Department of Defense (DoD), the Software and fonts are classified as "Commercial Computer Software" and the Government is acquiring only "restricted rights" in the Software, its documentation and fonts as that term is defined in Clause 252.227-7013(c)(1) of the DFARS; and
(ii) if the Software and fonts are supplied to any unit or agency of the United States Government other than DoD, the Government's rights in the Software, its documentation and fonts will be as defined in Clause 52.227 19(c)(2) of the FAR or, in the case of NASA, in Clause 18-52.227-86(d) of the NASA Supplement to the FAR.
