The Physics of a Fictional Star System

General physics and astronomy discussions not directly related to Celestia
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Riptokus
Posts: 4
Joined: 24.07.2009
With us: 15 years 3 months

The Physics of a Fictional Star System

Post #1by Riptokus » 25.07.2009, 17:33

I'm writing a piece of fiction, and have spent some effort trying to get some basic stellar mechanics correct. I am not that smart and am sure I've made quite a few mistakes, and am trying to find out what I need to work on to correct them. Any help would be appreciated greatly, Thank you!

Code: Select all

450100 "RCBWSun"      # The Star
{
   RA 100.100100      # An oddball fairly round number to ensure there is no conflict with something real.
   Dec 45.00      # An oddball fairly round number to ensure there is no conflict with something real.
   Distance 30      # An oddball fairly even number to ensure there is no conflict with something real.
   SpectralType "G6V"   # A G-6 Star. Main Sequence
   AbsMag 2.9463      # Luminosity 0.61 of the sun.
   Radius 615517.5
}


Code: Select all

"RCBWOne" "RCBWSun"
{
   Texture "mercury.*"
   Radius 3100.5                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         0.223463381245722108145106091718   # Length of year of 81.62 Earth days
      SemiMajorAxis      0.356               # Distance from primary star
      Eccentricity      0.069               # Eccentricity of orbit
      Inclination      4.05               # Orbital Plane Inclination
      AscendingNode      128.66               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      207.29               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      190.39               # Starting Location in orbit around the ecliptic.
   }

   # Obliquity 21                        # This Planet is Face Locked.
   Albedo 0.07                        # Planetary albedo
}

"RCBWTwo" "RCBWSun"
{
   Texture "mercury.*"
   Radius 2226.4                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         0.43033538672142368240930869267625   # Length of year of 157.18 Earth days
      SemiMajorAxis      0.550               # Distance from primary star
      Eccentricity      0.040               # Eccentricity of orbit
      Inclination      3.61               # Orbital Plane Inclination
      AscendingNode      168.04               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      332.08               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      336.05               # Starting Location in orbit around the ecliptic.
   }

   # Obliquity 19                        # This Planet is Face Locked.
   Albedo 0.07                        # Planetary albedo
}

ReferencePoint "RCBWThree" "RCBWSun"
{
   EllipticalOrbit
   {
      Period         0.66798083504449007529089664613279   # Length of year of 243.98 Earth days
      SemiMajorAxis      0.738               # Radius of orbit in AU
      Eccentricity      0.167               # Eccentricity of orbit
      Inclination      3.39               # Orbital Plane Inclination
      AscendingNode      61.76               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      65.41               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      107.38               # Starting Location in orbit around the ecliptic.
   }

   Visible true                         # Make the orbit and label visible
   Clickable true                        # Makes it selectable
}

"RCBWThreeAlpha" "RCBWSun"
{
   Texture "earth.*"
   Radius 7020.3                        # Equatorial Radius

   OrbitFrame {
      EquatorJ2000 { Center "RCBWSun/RCBWThree" }
   }

   BodyFrame {
      EclipticJ2000 { Center "RCBWSun/RCBWThree" }
   }

   EllipticalOrbit
   {
      Period         0.82666666666666666666666666666667   # Duration of the orbit in days
      SemiMajorAxis      38753.3414451            # Radius of orbit to Barycenter in KM
      Inclination      44.89               # Reducing the tilt of the orbit to equal the orbital plane of the Barycenter (23.5+Inclination) and then adding the appropriate inclination onto the system (18°)
      AscendingNode      0               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      0               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.  Not needed for Alpha and Beta.
      MeanLongitude      235.29               # Location in orbit. 235.89 is inverted in Beta's 55.89.
   }

   Atmosphere
   {
      Height 68                     # Darned if I know how to draw this border. Earth is at 60 with 1 Atm, Supposedly it drops in half for every 5 meters. 70 looks more than enough.
      Lower [ 0.43 0.52 0.65 ]               # Earth's numbers look fine.
      Upper [ 0.26 0.47 0.84 ]               # Earth's numbers look fine.
      Sky [ 0.40 0.6 1.0 ]                  # Earth's numbers look fine.
      CloudHeight 9                     # Increased pressure, put clouds a little higher
      CloudSpeed 50                     # Increased pressure would probably slow things down a bit.
      CloudMap "earth-clouds.*"
   }

   UniformRotation                        # Alpha and beta need to match so that they rotate as a single unit.
   {
      Period      19.84                  # 1 day = 19.84 Hours.
      Inclination   21.39                  # To orientate the equators properly. 3.39+18
   }

   Albedo 0.43                        # Planetary albedo
}

"RCBWThreeBeta" "RCBWSun/RCBWThreeAlpha"
{
   Texture "earth.*"
   Radius 6223.2                        # Equatorial Radius
   OrbitFrame {
   EquatorJ2000 { Center "RCBWSun/RCBWThree" }
   }

   BodyFrame {
   EclipticJ2000 { Center "RCBWSun/RCBWThree" }
   }

   EllipticalOrbit
   {
      Period         0.82666666666666666666666666666667   # Duration of the orbit in years
      SemiMajorAxis      48246.3987188            # Radius of orbit to Barycenter in KM
      Inclination      44.89               # Reducing the tilt of the orbit to equal the orbital plane of the Barycenter (23.5+Inclination) and then adding the appropriate inclination onto the system (18°)
      AscendingNode      0               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      0               # The spot on the orbital axis where the long axis of the orbital eccentricy is found. Not needed for Alpha and Beta.
      MeanLongitude      55.89               # Location in orbit. 55.89 to invert Alpha's 235.89
   }
   UniformRotation
   {
      Period      19.84                  # 1 day = 19.84 Hours
      Inclination   21.39                  # To orientate the equators properly. 3.39+18
   }

   Atmosphere
   {
      Height 59                     # .955 Atmospheres, less volume would probably shrink the size, although probably not by much.
      Lower [ 0.43 0.52 0.65 ]
      Upper [ 0.26 0.47 0.84 ]
      Sky [ 0.40 0.6 1.0 ]
      CloudHeight 6.8                     # Lower pressure would result in lower clouds
      CloudSpeed 67                     # Lower pressure would probably result in faster clouds
      CloudMap "earth-clouds.*"
   }
   Orientation [270 0 1 0]                     # Rotates the object 90 Degrees to fit with my custom texture
   Albedo 0.34                        # Planetary albedo
}

"RCBWFour" "RCBWSun"
{
   Texture "mercury.*"
   Radius 1939.5                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         1.424804928131416837782340862423   # Length of year of 520.41 Earth days
      SemiMajorAxis      1.222               # Distance from primary star
      Eccentricity      0.141               # Eccentricity of orbit
      Inclination      5.13               # Orbital Plane Inclination
      AscendingNode      200.03               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      38.54               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      277.85               # Starting Location in orbit around the ecliptic.
   }

   Obliquity 34
   RotationPeriod 37.60                     # Length of day
   Albedo 0.07                        # Planetary albedo
}

"RCBWFive" "RCBWSun"
{
   Texture "pluto.*"
   Radius 7169.9                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         4.4916358658453114305270362765229   # Length of year of 1640.57 Earth days
      SemiMajorAxis      2.628               # Distance from primary star
      Eccentricity      0.267               # Eccentricity of orbit
      Inclination      4.28               # Orbital Plane Inclination
      AscendingNode      213.42               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      36.36               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      113.95               # Starting Location in orbit around the ecliptic.
   }

   Atmosphere
   {
      Height 71
      Lower [ 0.65 0.26 0.65 ]
      Upper [ 0.84 0.23 0.84 ]
      Sky [ 0.1 0.3 1.0 ]
   }

   Obliquity 31
   RotationPeriod 14.37                     # Length of day
   Albedo 0.7                        # Planetary albedo
}

"RCBWSix" "RCBWSun"
{
   Texture "jupiter.*"
   Radius 44173.8                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         7.7033264887063655030800821355236   # Length of year of 2813.64 Earth days
      SemiMajorAxis      3.766               # Distance from primary star
      Eccentricity      0.181               # Eccentricity of orbit
      Inclination      3.64               # Orbital Plane Inclination
      AscendingNode      135.41               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      96.56               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      157.13               # Starting Location in orbit around the ecliptic.
   }

   Atmosphere
   {
      Height 200
      Lower [ 0.7 0.6 0.5 ]
      Upper [ 0.5 0.45 0.4 ]
      Sky [ 0.8 0.8 0.5 ]
   }

   Obliquity 34
   RotationPeriod 9.79                     # Length of day
   Albedo 0.46                        # Planetary albedo
}

"RCBWSeven" "RCBWSun"
{
   Texture "jupiter.*"
   Radius 90251.6                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         25.540506502395619438740588637919   # Length of year of 9328.67 Earth days
      SemiMajorAxis      8.381               # Distance from primary star
      Eccentricity      0.104               # Eccentricity of orbit
      Inclination      3.19               # Orbital Plane Inclination
      AscendingNode      188.41               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      111.64               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      52.80               # Starting Location in orbit around the ecliptic.
   }

   Atmosphere
   {
      Height 300
      Lower [ 0.7 0.6 0.5 ]
      Upper [ 0.5 0.45 0.4 ]
      Sky [ 0.8 0.8 0.5 ]
   }

   Obliquity 41
   RotationPeriod 6.59                     # Length of day
   Albedo 0.53                        # Planetary albedo
}

"RCBWEight" "RCBWSun"
{
   Texture "jupiter.*"
   Radius    32873.4                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         68.184449007529089664613278576318   # Length of year of 24904.37 Earth days
      SemiMajorAxis      16.114               # Distance from primary star
      Eccentricity      0.034               # Eccentricity of orbit
      Inclination      3.02               # Orbital Plane Inclination
      AscendingNode      311.66               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      307.61               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      89.92               # Starting Location in orbit around the ecliptic.
   }

   Atmosphere
   {
      Height 190
      Lower [ 0.7 0.6 0.5 ]
      Upper [ 0.5 0.45 0.4 ]
      Sky [ 0.8 0.8 0.5 ]
   }

   Obliquity 37
   RotationPeriod 14.89                     # Length of day
   Albedo 0.54                        # Planetary albedo
}

"RCBWNine" "RCBWSun"
{
   Texture "neptune.*"
   Radius    28138.2
   EllipticalOrbit
   {
      Period         156.23353867214236824093086926762   # Length of year of 57064.30 Earth days
      SemiMajorAxis      28.007               # Distance from primary star
      Eccentricity      0.046               # Eccentricity of orbit
      Inclination      3.67               # Orbital Plane Inclination
      AscendingNode      147.13               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      215.63               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      68.05               # Starting Location in orbit around the ecliptic.
   }
   Atmosphere {
      Height 130
      Lower [ 0.6 0.65 1.0 ]
      Upper [ 0.5 0.55 0.9 ]
      Sky [ 0.5 0.7 0.9 ]
   }

   Obliquity 45
   RotationPeriod 18.00                     # Length of day
   Albedo 0.52                        # Planetary albedo
}

"RCBWTen" "RCBWSun"
{
   Texture "mercury.*"
   Radius    5664.3                        # Equatorial Radius
   EllipticalOrbit
   {
      Period         326.84714579055441478439425051335   # Length of year of 119380.92 Earth days
      SemiMajorAxis      45.811               # Distance from primary star
      Eccentricity      0.206               # Eccentricity of orbit
      Inclination      5.30               # Orbital Plane Inclination
      AscendingNode      325.75               # Point where the orbit plane crosses the ecliptic plane heading from negative into positive.
      ArgOfPericenter      337.10               # The spot on the orbital axis where the long axis of the orbital eccentricy is found.
      MeanLongitude      173.06               # Starting Location in orbit around the ecliptic.
   }

   Obliquity 59
   RotationPeriod 25.32                     # Length of day
   Albedo 0.15                        # Planetary albedo
}


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selden
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Re: The Physics of a Fictional Star System

Post #2by selden » 25.07.2009, 17:58

There's a lot of code there and it would take a lot of work to decipher it.
I'd suggest starting with much simpler catalogs, get them to work, and then slowly add more objects.

What kind of mistakes do you mean?

Errors in the SSC file so it doesn't show anything?
If you turn on Celestia's "console log", it'll usually tell the location of the first such error.
Type a tilde (~) to see the log, type up- and down-arrows to navigate in it.

Incorrect values so objects aren't going where you want them?
You'll have to learn the uses of the various SSC directives.
There are users' guides on the MotherLode at http://celestiamotherlode.net/catalog/d ... ation.html

Incorrect values so objects aren't going where celestial dynamics would dictate?
That's more difficult. Some formulas are included on http://www.lepp.cornell.edu/~seb/celest ... eters.html
A program which calculates gravitational effects may be able to help with that, too.
e.g. GravitySimulator. See http://www.orbitsimulator.com/gravity/a ... /what.html
Selden

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Riptokus
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Re: The Physics of a Fictional Star System

Post #3by Riptokus » 25.07.2009, 19:31

Just the physics. I've got it functional in Celestia. I'm mostly worried about the stability of the orbits and how they interact. I worked a lot of it out over a long period of time, and some of it changed while I worked on it. I don't even remember how I came up with some of the information. Now that I have mostly together, I am about to go ahead and run with it, but before I do I want to be certain my science is sound, and where it isn't I need to fix it.

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selden
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Re: The Physics of a Fictional Star System

Post #4by selden » 26.07.2009, 10:55

People often use GravitySimulator (URL above) to study system stability. I've never done it myself. Perhaps someone experienced with the program can give some pointers.
Selden

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Riptokus
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Re: The Physics of a Fictional Star System

Post #5by Riptokus » 26.07.2009, 12:54

I'd definitely appreciate that. I attempted to work with Gravity simulator, but didn't have the slightest clue as to how to convert what I have to what it wants, or how to output what it generates for that matter. I didn't find any nice tutorials like I did for Celestia to work with it.

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selden
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Re: The Physics of a Fictional Star System

Post #6by selden » 26.07.2009, 18:01

The author of the program (tony873004) often posts to the Bad Astronomy and Universe Today forum at http://www.bautforum.com/

You might be able to contact him or find some usage notes there.
Selden

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Riptokus
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Re: The Physics of a Fictional Star System

Post #7by Riptokus » 27.07.2009, 02:26

Well, I've (I think) figured out how to get the gravity simulator to work. I've noticed some odd things...
Their included "full system" simulation played at a time step of 6 years seems to kick planets out of the system, while the same simulation played at 2048 seconds doesn't. This over the same time scale.

I am a little concerned with the accuracy of the Gravity Simulator due to that. Just the same, I put it together, I supplemented my Binary worlds of ThreeAlpha and Beta into one massive world with the radius of 'the combined distance to the barycenter of each world plus the radius of each world' and divided in 2 to get about 50121 Km.

The system, running at 2048 seconds, seems stable for 300 years so far and counting. I think, barring anyone coming up and saying I made some critical mistake in my math somewhere, that I will go ahead and call it correct (after leaving it running overnight to be sure no worlds end up ejected due to some unforeseen stellar alignment that might occur in a few thousand years). If anyone spots something wrong though, I would certainly appreciate being pointed in the right direction so I might spot it too.

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selden
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Re: The Physics of a Fictional Star System

Post #8by selden » 27.07.2009, 09:54

If you think the program has limitations, you should discus them with the author. You shouldn't be hesitant about it. I'm sure he'd be glad to explain what's going on. My personal expectation would be that the time step needs to be very short compared to the fastest orbit involved. I'd also expect that this kind of issue would be described on the web site.
Selden

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Hungry4info
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Re: The Physics of a Fictional Star System

Post #9by Hungry4info » 27.07.2009, 23:50

It does destabilize when you use large time steps because the computer simply can't run that epic fast, so it just calculates as many changes as it can amongst the simulated six years (or however high your timestep). For any gravity simulator, the shorter the timestep, the more accurate it will be. This is a limitation of computers themselves.

Gravity Simulator is nice, but I just use Systemic and let it run orbital stability algorithms (or whatever). Works pretty well for me.
Current Setup:
Windows 7 64 bit. Celestia 1.6.0.
AMD Athlon Processor, 1.6 Ghz, 3 Gb RAM
ATI Radeon HD 3200 Graphics

MKruer
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Re: The Physics of a Fictional Star System

Post #10by MKruer » 05.08.2009, 08:14

Do you have a link to the program Systemic? I am finding that Gravity Simulator is a pain if you want to make a system because you literally have to recreate the entire system every time you want to make an adjustment to the system.


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