Travel to Space/Travel to Space.iso/dos_prog/astronmy/dance/samples.scp

Text File | 1991-05-10 | 21KB | 382 lines

Dance Sample Simulations
objects.rsm
>>Introduction
Introduction to the Dance v2.3 Sampler

  Welcome to the `Dance of the Planets' sampler. This special demonstration
version of the program shows a wide selection of simulations illustrating much
of the detail and scope of Dance. In the samples you will see:

* A number of transient sky events- eclipses, solar transits, and occultations.
* Starry skies with constellations, grids, and Messier deep sky objects (DSOs).
  The full program has some 9100 stars (to 6.5 mag) and over 1300 DSO's.
* 20 selected asteroids and comets. The complete program has over 6000 -
  virtually all numbered asteroids and recorded comet `apparitions' thru 1990.
* All planets seen from afar, and closeups of Earth and Moon, and the Saturn
  system. Of course in the full program all the planets can be viewed up close.

  The sampler won't accept date input, except for the initializing dates used
in the examples. It can be set from 4680 BC to AD 9999 in the full program.
Even with these limitations, there is much to see and do- while pleasurably
learning Dance operation. On your first time through, follow the comments and
instructions on each screen, and press [Page Down] when ready for the next.

  [PgDn] now to proceed. At any time you can also press [Home] to see the
sampler contents, and from there, jump directly to a particular simulation.

                                              - Thomas Ligon  March, 1991

>>A Starship Perspective
SV>X>0>->100>0.5>-10>270>00000000000000000000>
A familiar sky but for the bright central star- the Sun, 3 light-days distant.
Press [s] to see orbits- use [s]+[shift] to fine adjust VGA `skylines'. Adjust
monitor brt/contrast for dark space with many stars (some 200 are on screen).
On Control Bar below, note date and ecliptic coordinates of this `Space View'.

>>Basic Viewing Operations
Space and Earth Viewing Modes.. Basic Viewing Operations

Space View (previous screen) is from outside the solar system. At 1X (next
 screen), the apparent size of constellations and S.S. are much as they would
 appear out a starship window 270 au from Sun.
Earth View (or Earth's Sky) provides views from a specified Earth `site' from
 which to watch motions/alignments of orbiting bodies against the starry sky.

* Simulation Pace, Zoom magnification, and View direction (latitude,longitude)
  are selected with hot key and changed with cursor keys. Active selections are
  highlighted, simulation is paused. Pressing any other key resumes simulation.
* The screen may be updated for each Zoom and View direction step, or only for
  the final viewing setup by toggling Loc on/off with [ScrollLock].
* View direction may be changed in 1° or 5° steps by toggling Ins on/off, or by
  using cursor keys with [shift] for 1°. (See next screen for Ins and Loc use.)
* SET PACE TO SUIT. Some of the following simulations will be too fast for some
  PCs, too slow for others. Very fast pace settings may reduce accuracy because
  fewer gravitational calculations are performed `per orbit' (steps too large).
* Objects on the screen can be labeled by using [L]abel from the control bar.
* MOUSE OPERATION- point and click selection, roll to change values, and click.
  Use right button as Esc (escape) from menus, return to previous, etc.
* EGA OPERATION- new views are composed on `back screen'; wait for quick change.

HELP ON MENU PROVIDES OPERATION GUIDE. Recommended.                 [PageDown]

>>Ins and Loc View effect
SV>X>1>->100>0.5>65>90>00000000000000000000>
(Looking towards Polaris) Ins & Loc affect view changes. For 1° view changes,
put Ins on (lit), or use shift+cursor keys. Toggle [Insert] key or point/click
Ins bar. Put Loc on (lit) for screen redraw for each zoom/view step. Toggle Loc
with [ScrollLock] or point/click Loc bar.        /INS bar        /LOC bar

>>The Solar System at 1X
SV>X>1>->100>1>-17>270>00000000000000000000>
Zooming in on the Solar System.  (Use keys or mouse point/click/roll for this)
With Loc off, press [z] to select Zoom, change to 4X using the cursor key, and
[Enter]. Label to identify planets. Increase Pace to see orbital motion-[Enter]
pace to resume simulation. Note clock/calendar. Try Zoom changes with Loc on.

>>Tracking Earth
SV>earth>1>03/26/1991>100>32>-3>144>00000000000000000000>
Tracking Earth- locked at the center (Label). At this view angle the different
orbital inclinations of the inner planets are quite evident. Planet motion is
suspended (note Lock-idle below) when tracking at low zoom. With Loc off, zoom
to 32kX (32000X) and press Enter to resume orbital simulation. Label Moon.

>>The Home Planet
EV>earth>0>03/26/1991/12>20>0.5>-3>144>0000000000000000000>
The Home Planet. Same view direction as previous screen, but now from special
Apollo viewpoint 250,000 km from Earth (inside Moon's orbit). Zoom to 2X (max).
Select Planet Grid from menu, shift-[s] to adjust VGA. Press any key to erase
grid. `More Options' on menu provides 2nd menu with cloud on/off toggle.

>>From the Earth's Sky
EV>X>1>01/01/1990>1000>0.5>-26>18h00>00000000000000000000>
In Earth's Sky.  View towards Sagittarius from Earth. Here is a grand planet
rendezvous in the morning sky, early Feb 1990. Identify with Label. Note View
declination, right ascension of center cross. Change Pace to suit & watch into
February. Sun's rays correspond to 1 hr from sunset/sunrise.

>>Constellations and Grids
EV>X>1>11/20/1991>1000>0.5>11>04h20>00000000000000000000>
Constellations & Grids. Press [f] for Find, type in Leo. Select ConstelDraw on
menu for lines. Adjust VGA with shift-[s]. To see right ascension and declina-
tion grid, select Celest Grid on menu. These skylines will remain in the sky
until toggled off on menu.

>>Ancient Guidestar
EV>X>0>03/21/-2850>10>0.5>75>00h00>00000000000000000000>
A familiar north sky, but note the date. Press [s] for skylines, Constels and
Grid on- dim for subtle effect. The Earth's axial direction precesses about the
ecliptic north, and at this time alpha Draco was the polar star. At 1X, you can
[L]abel this modest star. TURN OFF menu Constel and Grids for following page.

>>The Midnight Sun
EV>X>0>06/21/1991>0>min>0>06h00>00000000000000000000>
Midnight, summer solstice. To see sun from the north pole, select More Options
from the menu, and then site Coordinates. Enter 90,0 for 90N; longitude doesn't
matter! Now select Find and enter `north hor' to see the horizon position at
midnight. Increase pace and check the east horizon at 6 am. Change site Coords.

>>Christmas Stars
EV>X>0>06/17/-1>50>0.5>23.5>07h08>00000000000000000000>
LABEL. A number of celestial events around year 0 are Christmas star candidates.
Here is a rather splendid conjunction of Jupiter and Venus in the western sky,
June of 2 bc (Year -1 = 2 bc). Set site Coords to 31.5, 35.1 for Jerusalem and
reenter date. Zoom down to min and Find `west hor' at about 20 hours (8 pm).

>>DSOs and Messier Objects
EV>X>1>11/20/1991>1000>0.5>12>4h40>00000000000000000000>
The Messier catalogue of deep sky objects (DSOs) are mostly star clusters and
galaxies. Select DeepSky Objs from menu, press [M] or [Enter] to select. Press
Esc to exit menus. Select [F]ind and type in M31 for the Great Andromeda galaxy.
These DSOs are dim- adjust monitor? Label, zoom. DSOs stay on until toggled off.

>>Fixed Moon with Occultation
EV>moon>0>08/13/1990/18>50>2>40>-105>00000000000000000000>
If `fix moon' is typed into Find when viewing the sky, the moon will be found &
fixed at the center (already done here). Zoom to 8X and watch an occultation of
the Pleiades. When fixed on Moon, Sun or planet, use Esc to release tracking.
Site Coords on 2nd menu shows Colorado site. (Re-enter date if site changed.)

>>Lunar Eclipse
EV>moon>0>02/10/1990>50>8>-30>150>00000000000000000000>
The Moon passing through the Earth's shadow- viewed from Australia. The partial
shadow of the Earth, the penumbra, appears first at about 2:30 local time. In
this lunar eclipse simulation, a rusty `sunset' color leads into the deep shade
of the umbra. Due to atmospheric refraction, the Moon is never entirely dark.

>>The 1991 Solar Eclipse
EV>sun>0>07/11/1991/10>50>8>23.6>-110.8>00000000000000000000>
The Big One. 1991 solar eclipse as seen from La Paz, Baja California. Change
Pace to suit. Just before totality (around 11:45), slow to 1 or even `true'.
Note corona. Use Site Coords on `More Options' menu to check/change location.
If you change sites, select Date and re-enter 07/11/1991.

>>Venus Solar Transit
EV>sun>0>06/08/2004/06>50>16>30>31.2>00000000000000000000>
A Venus Solar transit viewed from Cairo. These are rare events- none occurred
in the 20th century; two will in the 21st. The next one is simulated here, and
begins at about 7:25 local time. Use Label to locate Venus before and after the
transit.

>>Virtues of Just Watching
EV>sun>1>03/15/1991>10k>0.5>40>-105>111111000>00000000000000000000>
Favorable apparitions (appearances) can be found in a number of ways with
Dance. Label to identify Mercury. The problem for it is finding near max solar
elongations. Here we fix on the Sun and watch. Note morning and evening
apparitions in May and July. Also the conjunctions with Jupiter, then Venus.

>>Viewing Planets Up Close
Viewing Planets Up Close

  Zoom and view the solar system from any angle, but the Sun will remain
central in `Space View' unless the Dance telescope is tracking a planet. To
view a planet up close, lock on by

 1) using the Planets menu (on main menu) or
 2) select the menu Target&Lock, place box over planet and press [Enter].

  The name of the tracked planet appears in the control bar. From the distant
space viewpoint you can zoom to 32kX magnification. Since from 270 a.u. all the
planets are approximately the same distance away, they will appear scaled to
one another. From Earth you can zoom to 512X. The apparent size of the planets
will be as they appear from Earth at that time.

  In the next screen Saturn is already locked in- shown with it are all the
asteroids & comets included with the sampler. (In such a Space View the planet
or Sun can be moved anywhere on screen using Move Center- 2nd menu.) So many
orbits take some time to calculate and draw, so there may be some pause.

>>Tracking on to Saturn
SV>Saturn>1>11/16/1989>200>16>-6>300>111111111>11111111111111110000>
Saturn locked on for close viewing- simulation idle at low zoom. Orbits of all
sampler asteroids/comets, as well as Phoebe, Saturn's outer-most satellite, are
visible. Move Saturn toward upper right using Move Center (2nd menu). With blue
cursor at desired spot, press Enter to move center. Adjust VGA Skylns. Label.

>>Saturn's Satellites
SV>Saturn>1>07/01/1990>200>1k>0>293>
Saturn's major satellites. At 1000X Phoebe's orbit is partly off screen. You
can [I]nvert for north to be down (note north-pointing arrowhead). Label to
identify the satellites. Zoom up and press any other key to resume simulation.

>>Saturn Up Close
SV>Saturn>0>11/16/1989/12>200>32k>0>343>S111111111111111111
Saturn at full power- Titan coming up from below. Toggle orbit skylines on/off.
Label satellites. Decrease View longitude to better see the rings- they darken
as they are viewed more from the back (VGA). At this time the rings are highly
tilted to the Sun, so Saturn casts a short shadow on the ring-satellite plane.

>>Saturn-star Occultation
EV>sat>0>07/03/1989>50>-512>59.3>18.3>00000000000000000000>
An Earth View of Saturn simulating the occultation of 28 Sgr, a 5.4 magnitude
star, as seen from Stockholm. This is the brightest star occulted by Saturn
known. From some locations in Europe, 28 Sgr slipped behind Titan as well!
(Star labels are skyline color, so put Skylns on and then Label the star.)

>>Comets Revealed
SV>X>1>06/15/1989>100>0.5>-13>90>00000000000101110000>
A small comet sampling as seen from afar. Note the two parabolic orbits. Such
comets, seen only once, may approach from any direction. Orbits of periodic
comets Halley and Encke are also present. Label at 4X to identify. Zoom to 16X,
turn off Skylines, set a high pace and watch the tails of the parabolic comets.

>>Halley Perihelion
SV>X>1>10/15/1985>1k>32>-10>330>111110000>00000000000100000000>
Comet Halley approaching perihelion. Adjust Pace and Skylines to better see the
developing tail. Halley moves north of the ecliptic only briefly, passing back
south between the orbits of Venus and Earth. Never close to any planet, its
orbit is relatively stable. View toward 90°S (from overhead) and re-enter date.

>>Halley Apparition                     123456789012
EV>X>0>12/25/1985>10k>0.5>-23>21h00>111110000>00000000000100000000>
Halley Revisited - An Earth view. The 1986 apparition wasn't great; you can see
why. Adjust Pace and watch while the comet passes through perihelion, Feb. 8,
1986 (your PC will bleep). Note the apparent speed increase as the comet angles
down for its southerly ecliptic plunge. Skylns off to better see tail.

>>Halley Loops
EV>X>1>06/01/1991>40k>0.5>3>09h20>111110000>00000000000100000000>
A Lingering Look at Comet Halley (Label). Below Leo you can to this day still
find Halley cycling its way to the far reaches of its orbit. Such epicycles are
due to the parallax caused by the Earth's orbital motion. Run the simulation
for several years. Run it backwards with a negative Pace, re-entering the date.

>>Orbital Simulation
The Simulation Nature of Dance

  Dance is an orbital simulator. This means that the program is constantly
calculating the gravitational effects of the various bodies on one another and
moving them accordingly. In the program `real' distances, masses and velocities
are operating according to Newtonian gravitation in three dimensional space,
and the results are scaled and transformed to the screen. Dance is a detailed
working model of the solar system that can not only show views and events that
are calculable, but also simulate perturbations and other complex multiple-
bodied orbital interactions that are generally not. Being able to predict orbit
changing encounters of the past and future is an exciting and unique aspect of
Dance. With the full database of asteroids and comets you can discover events
and causes that few if anyone else knows about.

  The next simulation shows an interesting future event with comet Kojima.
Discovered in 1970, Kojima has a period of nearly 8 years, and has been very
regular for three apparitions. During the encounter, simulation will slow as
Dance performs more calculations to maintain accuracy. The strongest change to
the comet's orbit will be an increase of inclination to the ecliptic plane.

>>Comet Futures
SV>X>1>09/01/1995>40k>8>-35>90>111111000>00000000000010000000>
A Strong Perturbation. Kojima's orbit, like most periodic comets, is chaotic.
Simulation reveals a strong orbit-changing Jupiter encounter during 1996-1997.
Result: an earlier, brighter apparition. Encounter distance (in planet radii)
will appear upper left. Jupiter's outermost satellites are out about 320 radii.

>>Bright Asteroids
SV>X>1>09/20/1990>5k>8>-90>90>111110000>11111000000000000000>
`Bright' Asteroids (dim VGA Skylines to see). Ceres is the largest; over 900 km
diameter. Only Vesta is ever brighter than mag 6. Vernal equinox direction (0°
Longitude) is shown when viewing toward 90° N/S. View toward 10°S and note the
orbit of Pallas. Object Status (Access menu) gives observation data for date.

>>Some Asteroid Extremes
SP>X>1>01/09/1991>20k>8>-13>120>111111100>00000000110000000000>
At the time of their discovery, asteroids Hidalgo and Icarus traveled farthest
and closest to the Sun. Label to identify. Zoom to 32X, pace 40k-80k, to see
Icarus zipping through perihelion. Turn View toward 90°S. Move the Sun upward
get all of Icarus's orbit on screen using Move Center (More Options menu).

>>Asteroids in the Sky
EV>X>1>03/01/1989>20k>0.5>-33>18h00>111111110>00111000000000000000>
Asteroids In A Starry Sky- looking towards Sagittarius from Earth in 1989. The
motion and paths of several bodies are seen. Watch the epicycles through 1989.
Planet coordinates are on the [A]ccess screen; asteroid position/magnitude
on the Object Status screen. In June-July Vesta was at maximum brightness.

>>Asteroid 1989FC
SV>X>1>02/01/1989>2000>64>-20>45>111110000>00000000001000000000>
Our brush with asteroid 1989FC was closest known at the time, 400,000 miles in
March of 1989. Though small, 1989FC would have caused havoc had it struck. Dim
and fast moving, Earth-crossers are hard to find. You can check out dozens in
Dance. Slow pace in mid-March and note date and minimum distance (Earth radii).

>>Orbital Resonances
Orbital Resonances

  Asteroids with periods that are a simple ratio to Jupiter's are regularly
perturbed by it. Such resonances have depopulated the Kirkwood gaps, that is,
asteroids with periods near these resonant values are not found. But resonances
with ratios near one can provide an island of orbital stability. These `island'
resonances provide one classification for Asteroids. Trojan asteroids, with a
ratio of 1:1, essentially share Jupiter's orbit. In this `Lagrangian resonance'
the asteroid is nominally 60° ahead or behind, never getting too close. There
are over 100 Trojans known. Hildas are another large group with 3:2 resonances.

  Resonances are also found among the satellites of the Jovian planets. The
Galilean satellites have period ratios very nearly 1:2:3:4 (check the Access
Satellites screen for Jupiter when planet tracking). Like the hands of a clock,
they have regular `meeting places'. The Saturnian system is full of resonances,
including co-orbital satellites with Lagrangian resonances.

  When you have the Saturn system on the screen in some of the following simu-
lations, press [A]ccess and select Satellites from the menu. Note the periods
for co-orbital satellites and other resonances. Esc to return to the simulator.

>>Tuned Asteroids
SV>X>1>08/01/1988>40k>8>-90>270>000010000>00000111000000000000>
Asteroid Resonances- Living with Jupiter. (Dim VGA Skylns. Inner planets are
off for speed.) Some stable resonances: Hilda, the first 3:2 resonance found;
Achilles, the first 1:1 Trojan asteroid. Thule, the only known 4:3, is quite
perturbed every 3 Jovian (36 Earth) years. Watch through 2018. Pace to suit.

>>Tuned Satellites
SV>Saturn>1>07/01/1990>5k>4k>-70>35>S000000000000001100>
Satellite Resonances (Dim VGA Skylns or toggle orbits on/off to see Hyperion.)
With a 3:4 resonance, Hyperion avoids strong perturbation from Titan by being
near maximum separation whenever they pass. The influence still causes pre-
cession of Hyperion's orbit. Inner satellites are off for speed.

>>Doing Orbital Experiments
Doing Orbital Experiments

  Orbital elements of real or hypothetical objects orbiting the Sun can be
placed in a text file and loaded into Dance. On the next screen you will see
four hypothetical objects with the same period but with very different eccen-
tricities. Such examples can vividly illustrate basic principles of orbital
mechanics. An introduction to the basic theory, along with simulation examples,
can be found in the Dance manual.

  Examples of other enlightening experiments: 1) using hypothetical objects to
see whether regularly spaced, nearly circular orbits between the Jovian planets
are stable. 2) How, with a `primordial' distribution of asteroids (near-circu-
lar and regularly spaced), the Kirkwood gaps arise. Such experiments involve a
lot of objects and time. A reasonably fast PC with coprocessor is recommended.
Very long simulations can be saved in Resume files and run over several nights.

>>Hypothetical Asteroids
SV>X>1>->20k>8>-90>90>000000000>00000000000000001111>
Four hypothetical objects with the same period. Note the semimajor axes are the
same- from basic orbital theory, the period is determined solely by the semi-
major axis and mass. The four start together (note perihelion `blip' sounds).
Set pace to 240k and note any accumulative simulation error by spread in blips.

>>Ordering and Updates Info
Ordering and Updates                                       May 10, 1991

DANCE OF THE PLANETS, version 2.3, is available for $195 plus shipping. Future
versions may be subject to price increases. Please order from:

     A.R.C. Software
     P.O. Box 1955E
     Loveland, CO 80539

     For information or ordering call 1-303/667-1168, or fax [phone]. MC/VISA
accepted as well as authorized purchase orders. Postage paid on domestic orders
paying by check or money order. Foreign orders must be prepaid (charge cards
accepted) and include shipping and handling- $15 for Canada and Mexico, $25 for
Europe plus other western hemisphere, and $35 for eastern hemisphere.

>>The Southern End
EV>X>1>->100>0.5>-70>12h40>111111111>00000000000000000000>
The end of the sampler and a nice view of the southern sky. Select celest Grid
from the menu and adjust for subtle skylines. Then press [Home] for contents,
from which you can go to any sampler simulation. From the contents you can also
exit the sampler script and go on your own. Check out 3-D orbits from space.