Libris Britannia 4/science library(b).zip/science library(b)/ASTRNOMY/DANCE13.ZIP/DEMO.DOC

Text File | 1990-02-16 | 21KB | 450 lines

                    Dance of the Planets(TM)
                      Demonstration v1.30
                       December 5, 1989


WHAT IS DANCE OF THE PLANETS?

  DANCE is a computer model of the solar system. It is a realistic
model with correct scaling, image details and lighting effects. It is
a working model, combining orbital simulation with accurate time-
location calculations. It is a three-dimensional model in which scenes
can be viewed from any angle, and bodies interact gravitationally in
three-dimensional space. It is a complete model with virtually all the
known bodies of the solar system which, in addition to the Sun and
nine major planets, includes 60 satellites, over 4100 asteroids, and
some 1400 recorded comet appearances. The model is also an observation
tool, providing views of all the orbiting bodies against the starry
sky as seen from Earth, complete with location coordinates for any
time. The intent is to represent the solar system in a deep and de-
tailed manner that does some justice to the richness and complexity of
the real thing. To make it very accessible through the power of the
computer.


WHY ORBITAL SIMULATION IS IMPORTANT

  Behind the images, the never-ending task of the program is to simu-
late (mimic) gravity by constantly calculating the gravitational
effects that each body has on the other, and allowing them to move
through space accordingly. This "working" model can therefore antici-
pate and reproduce motions, positional relationships, precessions, and
many strong perturbation events that have or really will occur "out
there". It doesn't know where a chaotic comet will be 50 years from
now in the sense that it can calculate it. But by simulating gravity
with greatly accelerated time, you can just let it happen and see
where the comet will be. Equally well, you can run time backward and
see where an object was in the past, and what influences caused it to
be where it is today. Orbital simulation provides something of a time
machine, and can vividly illustrate orbital phenomena.


WHAT DOES DANCE DEMO DO?

  The demo presents a selection of simulation scenes chosen to illus-
trate the range and nature of DANCE. Within limits, you can operate
the demo just as you would the complete program. Between the examples,
you will find some explanatory text to amplify what you are seeing.


RUNNING THE DEMO

* Place the disk in your drive and select that drive (for example,
enter a: to the DOS prompt).

* Enter DANCE to load and run the program.

* After the title screen, press PAGE DOWN to begin the demo (a demo
script is ready to go).

  Now go through the demo at your own pace using the PAGE keys. HOME
shows the script contents. Change viewpoint and magnification if you
wish, or any other side excursion. Note:

* The apparent simulation SPEED is dependent upon the PC on which it
is run. Change the SPEED settings to suit your system. Perhaps slow it
if you have the coprocessor, or speed it up if you don't. There will
be further notes in the demo in regard to speed.

* The scenes have captions which may be erased by view changes you
make. You can restore the caption by pressing ENTER when the simula-
tion is running (PAUSED.. doesn't appear after the date), or just
continue the demo by pressing PAGE DOWN.


      READ THE FOLLOWING FOR BASIC DEMO CONTROL & OPERATIONS


ESSENTIALS THAT YOU NEED TO KNOW.

  You don't need to do much to run and enjoy the demo, but you will
get more out of it if you interact with it. DANCE also assumes, but
does not require, some practical knowledge about the subject matter
(coordinate systems, orbital phenomena, etc.). The complete manual
explains the basic terms and concepts.

  Here are some basic demo operating considerations that you need to
keep in mind.


SPEED
  The speed you perceive is dependent upon how fast your PC can
"crunch" numbers. If you have a fast PC with a coprocessor, some of
the demo simulations may need to be slowed down. If they are too slow,
increase the speed. But keep in mind that simulation accuracy suffers
at high speed settings because fewer calculations are being performed
to approximate the continuous effects of gravity. What is too fast
depends upon the particular objects being simulated.

  A coprocessor is always recommended for calculation intensive soft-
ware like DANCE. Fast (20mhz or better) 286 and 386 PC's perform okay
without, but better with. Coprocessors can speed performance by 5X-
10X. ARC can supply coprocessors made by IIT which are significantly
faster than Intel's, and similarly priced. A coprocessor is a good
hardware investment.

GOING BACK IN TIME
  Although the demo doesn't allow you to change the date, you do have
some control over time:
* To start a simulation over again, press DATE (press the 'D' key) to
get the initial date, and press ENTER. You may want to refresh the
screen by also pressing ERASE.
* You can always run the simulation (time) backwards by setting the
SPEED to a negative value.


CHANGING THE VIEW
  In addition to speed, you are encouraged to vary your perspective by
changing magnification (ZOOM), latitude, and longitude (ROTATE). If
you do this from the control bar (the hot key selections along the
screen bottom), the screen will be updated every time you make a
change with the cursor keys. This may be what you want, but it will be
slow on some PC's. The view can be changed directly to what you want
without intermediate screens by using the popup MENU.


FAST CHANGES FROM THE MENU
  Press MENU to pop it up, and then hold the HOT KEY to select the
parameter. It's value will be highlighted at the bottom of the screen.
Change this with the cursor keys. Press ENTER to accept the change,
and then select another menu parameter, or press ENTER a second time
to erase the menu and resume simulation.

Note: any time a parameter value is high-lighted at the bottom of the
screen, simulation is suspended and PAUSED.. appears to the right of
the calendar.


RESTORE THE DEMO CAPTION
  Making screen changes will erase the demo script remarks in the
light-blue box. You can restore this by pressing ENTER when the
simulator is running (not paused for other changes). Alternately, just
pressing PgUp or PgDn will go on to the last or next demo simulation.


MODES
  Program viewing and operation will be in respect to one of the
following three modes:

   SPACE MODE, in which the solar system is viewed from afar, from any
   angle (the default mode).

   PLANET MODE, which is still viewing from afar but as if with a
   powerful telescope locked onto the planet of interest (TRACK pro-
   vides a cursor that is moved over the planet. Lock on with ENTER).
   The name of the tracked planet will appear at the bottom of the
   screen in the control bar.

   Note: When in PLANET MODE only the planet and its satellites are
   active. Even if, at low power, other solar system objects are
   visible, they will not orbit, nor will they be IDENTIFIED.

   EARTH MODE, in which objects orbiting in the simulator are seen
   from an Earth-centered perspective. (EARTH VIEW is an on/off toggle
   on the popup MENU).


USING IDENTIFY
  IDENTIFY on the popup MENU is used to label objects on the screen.
This pauses the simulator, and then any key press will erase the
labels and resume simulation. When in PLANET MODE, only satellites are
labeled, even though at low power (ZOOM) other objects may be seen.


USING ACCESS
  ACCESS in SPACE or EARTH MODE will display planet coordinates/para-
meters and a second (ACCESS) menu. OBJECT STATUS can be chosen from
this menu to show orbital parameters and coordinates for any asteroid/
comet active in the simulator. Both planets and asteroids/comets can
be made temporarily inactive in the simulator to improve speed. This
is done for planets with the ACTIVE PLANET selection on the ACCESS
MENU, and other objects can be toggled on/off on the OBJECT STATUS
screen. In either case, when the object is inactive, the first charac-
ter in its line will be 0.

  ACCESS in PLANET MODE shows a table of satellite information. The
different planet systems can be compared by pressing the PLANET NUMBER
as indicated at the bottom of the screen. Although the demo is limited
to Saturn for close views, in the full program you can go directly to
the planet by then pressing 0 (GOTO).


VIEWING ORBITS IN 3D
  Orbits are drawn in stereo pairs when 3 D Orbits is toggled on on
the popup MENU (toggle 3 once again to restore normal viewing). 3-D is
useful for understanding relative orbit orientations which can be a
very important factor in perturbations and orbital stability. Simula-
tion is paused when in 3-D. (Note: plastic framed color filter glasses
are included with the full program.)

  Not everyone can see the 3-D effect because of vision asymmetries.
But most can with a little practice. Try to see the same background
color with each eye. You can control the degree of stereo separation
with the VIEW (apparent distance in cm) selection on the control bar.


USE HELP
  Selecting HELP will provide a quick reference guide to DANCE control
bar and menu selections.

The remaining documentation is excerpted from the DANCE manual. The
contents provide an overview of the scope of v1.30.



TABLE OF CONTENTS FROM THE COMPLETE DANCE v1.30 MANUAL


                      PART 1: USING THE PROGRAM

INTRODUCTION
 About DANCE OF THE PLANETS........................................1-1
 About This Book...................................................1-2
 About Disks and Installation......................................1-2
 Dance in Your PC..................................................1-3

FIRST LIGHT
 The Dance Screen and Control Bar..................................1-4
 The Control Bar Selections........................................1-4
 Getting to Know the Dance Environment.............................1-5
 The Main Menu.....................................................1-7


A DANCE TOUR OF THE SOLAR SYSTEM

STAR NAVIGATION
 The Starry Sphere.................................................1-8
 About Coordinates.................................................1-9
 Orientation to the Vernal Equinox................................1-10
 The Celestial Sphere Overlay.....................................1-10
 Viewing From Earth...............................................1-10
 Observing the Polar Sky..........................................1-11

VISITING PLANETS
 Basics for Planet Viewing........................................1-12
 A Voyager View of Saturn.........................................1-12
 Light, Color, and Your Monitor...................................1-13
 Viewing from Earth...............................................1-13

OBSERVING ASTEROIDS AND COMETS
 Plotting Asteroids...............................................1-14
 Resume Files.....................................................1-15
 Asteroids from a Resume File.....................................1-15
 Orbit Initialization and Epoch Currency.....................1-16,1-17
 Asteroids from the Earth.........................................1-17
 Inactivating Objects in the Simulator............................1-18
 Deleting Objects from the Simulator..............................1-18
 Getting Asteroids from the Main Files............................1-18
 Four Instructive Comets..........................................1-19
 Viewing Orbits in 3-D............................................1-20
 Getting a Better View of Comet Halley............................1-21
 Comet Kojima In Commotion: a strong perturbation.................1-22
 Reality and Accuracy of Orbital Simulations.................1-23,1-24
 A Sense of Scale and Time........................................1-24


ACCESS: THE OTHER SIDE OF DANCE

ACCESS FOR INFORMATION AND CONTROL
 Access from the Solar System.....................................1-25
 The Access Menu..................................................1-26
 Access to Orbit Information......................................1-27
 Orbital Elements and Simulator Orbits............................1-27
 Object Coordinates...............................................1-28
 Access to Planet Systems.........................................1-28
 Fast Access to the Other Planets.................................1-29
 Saving a Planet Resume File......................................1-29

HARDWARE ISSUES
 CPU Performance..................................................1-29
 Help for Slow Simulations........................................1-30
 Printing the Access Information Screens..........................1-30
 Dumping the Graphic Screen.......................................1-30


                       PART 2: THE SOLAR SYSTEM

FORMATION, CELESTIAL MECHANICS, AND THE INNER PLANETS

FORMATION AND THE CHARACTER OF THE SOLAR SYSTEM
 Introduction.....................................................2-1
 The Formation of the Solar System................................2-2
 The Solar System Today...........................................2-3
 Some Apparent Difficulties.......................................2-4

UNDERSTANDING THE MOTION OF THE PLANETS
 Pioneers and Kepler's Laws.......................................2-5
 Newtonian Mechanics..............................................2-6
 Newtonian Gravity................................................2-6

AN ORBITAL PRIMER
 Introduction.....................................................2-7
 Geometry and Dynamics of Elliptical Orbits...................2-7,2-8
 Orbital Energy and Velocity......................................2-8
 Illustrating Principals with Examples............................2-9
 The Orbital Elements............................................2-10
 Simulating Gravity in a computer......................2-11,2-12,2-13

ORBITAL STABILITY
 Precessing Nodes................................................2-13
 The Stability of the Solar System...............................2-14
 Orbital Chaos...................................................2-14


THE INNER SOLAR SYSTEM

INTRODUCTION
 Image Simulation in DANCE.......................................2-17
 Thinking Metric.................................................2-17
 The Inner Planets...............................................2-18
 The Sun.........................................................2-18

MERCURY AND VENUS
 Introduction....................................................2-19
 Good Apparitions and a Great Morning Rendezvous............2-19,2-20
 Christmas Stars.................................................2-20
 Viewing the Inner Planets at High Power.........................2-21

THE EARTH-MOON SYSTEM
 Introduction....................................................2-23
 Mars Epicycles..................................................2-24
 Martian Satellites..............................................2-24
 Fear of Phobos Falling..........................................2-24
 Are They Asteroids?.............................................2-25


                      PART 3: THE JOVIAN PLANETS

 Introduction.....................................................3-1

SATELLITES OF JOVIAN PLANETS
 Introduction.....................................................3-1
 Instability and Roche Limits.....................................3-2
 Formation and Proto-Satellite Swarms.............................3-2
 Tidal Forces.....................................................3-3

THE JUPITER SYSTEM
 Introduction.....................................................3-4
 Jupiter at Full Power............................................3-5
 Jupiter's Rings..................................................3-5
 The Satellites of Jupiter........................................3-6
 The Galilean Moons...............................................3-6
 Comparing Satellite Systems......................................3-7
 The Wild Outer Satellites........................................3-7
 Computer Escape Velocity?........................................3-8
 Are They Captured Asteroids?.....................................3-8

THE SATURN SYSTEM
 Introduction.....................................................3-9
 The Planet Saturn...............................................3-10
 The Rings of Saturn.............................................3-10
 The Satellite of Saturn.........................................3-11
 Resonances and Co-Orbital Satellites............................3-11
 Saturn's Irregular Satellites...................................3-12

THE URANUS SYSTEM
 Introduction....................................................3-13
 Comparing Jovian Systems........................................3-13
 The Planet Uranus...............................................3-14
 The Rings of Uranus.............................................3-14
 The Satellites of Uranus........................................3-14
 Conjecturing on the Tilt........................................3-14
 The Satellite System Edge-On....................................3-15

THE NEPTUNE SYSTEM
 Introduction....................................................3-15
 The Planet Neptune..............................................3-16
 Exotic Orientations in 3-D......................................3-16
 Comparing Satellites............................................3-16
 Triton..........................................................3-16
 Nereid..........................................................3-17
 Six `New' Satellites............................................3-17
 Arcs and Rings..................................................3-18
 Speculation about the Neptune Satellite System..................3-18

PLUTO AND CHARON
 Introduction....................................................3-18
 Viewing Pluto-Charon............................................3-19
 A Fortuitous Time...............................................3-19
 The Character of Pluto..........................................3-20
 Positional Accuracy of Pluto-Charon.............................3-20


                     PART 4: ASTEROIDS AND COMETS

ASTEROIDS

 Introduction.....................................................4-1
 Early History, Briefly...........................................4-2
 Origin and Nature of Asteroids...................................4-2
 Nature and Classification........................................4-3
 A Perspective on Asteroids.......................................4-4

ORBITAL CHARACTERISTICS OF ASTEROIDS
 Introduction.....................................................4-5
 Identifying Asteroids in a Plot..................................4-6
 Kirkwood Gaps................................................4-6,4-7

ORBITAL CLASSIFICATIONS
 Inner Asteroids..............................................4-7,4-8
 Distant Asteroids................................................4-9
 Asteroid Families...........................................4-9,4-10

OBSERVING ASTEROIDS
 Introduction....................................................4-10
 Magnitudes......................................................4-11
 Using DANCE to Find Favorable Oppositions.......................4-11
 Identifying an Asteroid in the Sky..............................4-11
 Identifying and/or Avoiding an Unexpected Asteroid..............4-12
 Further Exploring in the Data Files........................4-12,4-13


COMETS

 Introduction....................................................4-14
 Short-Period and Long-Period Comets.............................4-14
 The Origin and Nature of Comets.................................4-14
 Formation of the Oort Cloud.....................................4-15
 Star Drops......................................................4-16
 Telling Asteroids and Comets Apart..............................4-16

COMETS IN DANCE
 Introduction....................................................4-17
 Comet Simulations...............................................4-17
 Parabolic Comets and an Historical What-If.................4-18,4-19
 Oterma: The Case of a Lost Comet................................4-20
 Checking Simulator Accuracy.....................................4-21
 Oterma and the Hilda Asteroids..................................4-22
 A Comet Capture by Jupiter......................................4-22
 Observing Close Encounters from Earth...........................4-23
 Periodic Comets of Only One Appearance..........................4-24
 More Strong Perturbations.......................................4-24

WRITING YOUR OWN SUBJECT FILES...................................4-25
 A 10,000 year Simulation........................................4-26


BIBLIOGRAPHY
GLOSSARY
INDEX