 
 SOLAR SYSTEM ORRERY 
 

 Program created by Eugene Villar (SEAV)
 E-mail: (evillar@geocities.com)
    URL: http://www.GeoCities.com/SiliconValley/Horizon/2586/

 Copyright (C) 1996-1998, SEAV Softwares


 CONTENTS
 

   Overview
   Keyboard Controls
   The Screen
   The Perpective Types
   The Earth Fly-by Phenomenon

                              

 OVERVIEW 
 
  olar System Orrery is a simulation program that displays
   the planets of the solar system 3-dimensionally as they
     move around the sun.
       Various aspects of the program can be changed and va-
       ried to give different views and angles on the motion of
       the planets around the sun.

       NOTE: This program is only a simulation and does not pre-
          dict the actual position of the planets in their 
          orbits. Also, Pluto is not included since its orbit is
          too skewed and would make computing its position a
          problem.
                                                    
                              --

            
 KEYBOARD CONTROLS
 
  he different settings of the program can be changed dyna-
      mically as the program is being run. You can set the
      simulation speed as well as the position and range of the
      viweport. There are also other switching variables that
       control various other aspects of the program such as the
       type of perspective and the type of labels displayed with
       the planets.
          The keys used to control the program are the following

       Simulation Speed
       ----------------
           +: Increase
           -: Decrease
         SPC: Skip 5 days

       Viewport distance from the sun
       ------------------------------
          UP: Decrease (go closer)
        DOWN: Increase (go farther)

       Viewport tilt from ecliptic
       ---------------------------
        PGUP: Tilt up
        PGDN: Tilt down

       Viewport view angle
       -------------------
        HOME: Increase (wider)
         END: Decrease (narrower)

       Switching keys
       --------------
        TAB/F5: Switch between the two types of
                perspective (Z-type/Angular)
            F6: Switch the display mode of the
                Viewport windows (On/Off)
            F7: Switch between the different
                types of planet labeling
                  (None/Name/Number)

                              --


 THE SCREEN
 
  he screen is set up with the time and settings diplayed
      on the left bar while the main action is on the right
      side. The left bar displays the date and time, which is
      not actual. This is only a simulation. The time and date
       is merely for reference.
          On the right side, the main window, called the
       Viewport, displays a perspective view of the solar sys-
       tem. The two narrow windows at the right and bottom of
       the viewport shows where the Viewport is located and how
       wide it is "seeing" in relation to the solar system.
       These side windows can be toggled using F6.
            
                              --
         

 THE PERSPECTIVE TYPES
 
  here are two type of perspective in the program which you
      can select from as the program is being run. These are
      the Z-type and the Angular type.
         The Z-type is the perspective used most often in
       computer graphics. I call it the Z-type because the
       objects are scaled based on what their distance is (Z)
       from the viewport. Thus, objects farther away appear
       smaller and closer together.
          The Angular type is based on the angular position of
       the objects with respect to the viewport. This means that
       if the viewport is 60 wide, objects at 30 from the cen-
       ter of the view appear halfway from center of the window
       to the edge.
          If you set the view angle to 180, you can get to
       "see" behind you. The Angular type should be viewed with
       a circular window, but since the window is square, the
       areas near the corners of the window will display objects
       beyond the view.
          Moreover, as the view angle becomes smaller and smal-
       ler, the view using the two perpective types become
       closer and closer to each other. At 15, there is vir-
       tually no difference between the Z-type and the Angular
       type of perpective.

       TRIVIA: The 180 Angular view is also known as the
          Fish-eye view.

                              --


 THE EARTH FLY-BY PHENOMENON
 
  eing 3-dimensional, I included the size of the planets as
  a factor in displaying them. Now this would seem nonsen-
     sical since the planets would only be dots, and you can't
   get close enough to the planet to see them as disks.
       Well, you CAN see the disks of the planets, you just have
       to know how.
          The "Earth Fly-by" is the most interesting phenomenon
       involving this size factor and I discovered it while
       playing with the program. In the Earth Fly-by, you get to
       see earth zoom in front of you and you get to appreciate
       how fast the earth really goes around the sun.
          To view this phenomenon, change the settings to:

                   Run speed: 1 day
             Perpective type: Angular
                  View Angle: 180
            Distance fr. sun: 1.00004 AU
           Tilt fr. ecliptic: +3

       Notice that the earth zooms the screen when it's near the
       bottom at these simulation settings. If you decrease the
       tilt to 0, the earth would seem to wrap around the left
       edge to the right.
          Actually, the speed is so fast that the earth traver-
       ses the distance of the window in a single turn. Go back
       to the +3 tilt.
          Now, all you have to do is to slow down the run speed
       as the earth approaches the left side of the screen and
       keep on deccelerating until the speed is at 0.000195 days
       and the earth is very near the bottom of the window. When
       the earth is very near the bottom, decrease the speed to
       0.000024 days and decrease the tilt to 0. You should
       then see the earth on the left side of the window. Now
       all you have to do is to wait and see the earth's disc
       become larger and the earth zoom across the window.
          If you don't succeed in seeing it, try again!

          Compared with the earth's size, the speed of the earth
       as it goes around the sun is very fast indeed. And the
       simulation is going about a third as fast as actual time
       at 0.00024 days!
          (If you're not interested in astronomy, then this bit
       of an experiment would certainly not interest you one
       bit. Shame on you!)
          Similar effects could be achieved with other planets,
       but they're not as spectacular as the Earth Fly-by!

         :)

                              --


 
 Eugene Villar


