Help with a new planet orbit

[MKruer]

I am trying to create a planet that is tilted ~90 degrees off its axis, but at the same time, I want the poles to be sidereal to the star. AKA I want one pole of the planet facing the star while it rotates. How would I get this to work? The planet is spinning on 2 axis’s.

-TIA-

[Don. Edwards]

How about copying most of the Uranus info into your add-on .ssc and then modify it to your needs. That way you have a ready made planet with just a little tweaking to do.

Don.

[MKruer]

Already done, but that still does not tell me how to spin the planet on 2 axis’s.

[ElPelado]

you have to put this values:
inside "EllipticalOrbit {", put "Inclination 90"
and then(not in EllipticalOrbit), put "Obliquity 90".
i think that will help.

[granthutchison]

You need to use PrecessionRate to get this effect.
Here's a little test object in orbit around Sol, with its north pole directed always towards the star:

Code: Select all

"Test" "Sol"
{
   Texture "mars.jpg"
   Radius 1000

   EllipticalOrbit {
      Period          1
      SemiMajorAxis   1
   }

   RotationPeriod          24

   Obliquity               90       #tilted by 90 degrees

   EquatorAscendingNode    270      #N pole facing star

   PrecessionRate          0.985647 #degrees/day = 360/(Period*365.2422)
}


PrecessionRate needs to be in degrees/day, whereas Period is in years, so you need to convert your chosen period to a required PrecessionRate as shown.
If you've defined an AscendingNode, ArgOfPericenter and/or MeanAnomaly for your planet's orbit, you'll need to adjust the EquatorAscendingNode I've given. If your orbital Inclination is pretty small, of the order of a few degrees, then you can get a pretty good fix as follows. For north pole pointing at the star:

EquatorAscendingNode = AscendingNode+ArgOfPericenter+MeanAnomaly+270

For south pole pointing at star, it's the same equation less 180 degrees:

EquatorAscendingNode = AscendingNode+ArgOfPericenter+MeanAnomaly+90

If you have a high-Inclination orbit then things get slightly trickier - feel free to get back to me.

Grant

[MKruer]

Thanks that just what I was looking for.

Now I guess the question I should have asked first is how to add a new star/system not currently in Celestia.

Placement is irreverent for now. But with the 1.3 version I am not sure if Chris added the ability to add stars outside the dat files. I done some searching on the forums, but the last message I have found on the subject are over a year old.

And that reminds me of one additional thing. Do you have any clue on what the diameter of a planet that is about 8.5 more massive then Jupiter would be? In theory Jupiter is just about as large in diameter as a gas planet can be. If more material were to be added, it would be compressed by gravity such that the overall radius would increase only slightly.

If you care here is the excel spread sheet I am using to build the system.
http://www.linkline.com/personal/mkruer/Rylix%20System%20Information.xls

Let me know what you think.

[granthutchison]

Have a look at this thread http://shatters.net/forum/viewtopic.php?t=2323 and you'll see an example of the format for an *.stc file.

The theoretical curve for 4.6 billion-year-old gas giants maxes out at about 3 Jupiters, radius 75,000km. By 8.5J it's down around 72,500km.
If your system is younger you can go a little bigger than that.

BTW: Since you're striving for accuracy, do you have a mechanism in mind for the odd synchronous precession of your planet? It's not something that's at all likely to occur in nature.

Grant

[selden]

Grant,

Can you provide a reference for a planetary mass/diameter/age model? I was looking for one a few weeks ago and couldn't find it anywhere...

Thanks.

[granthutchison]

Can you provide a reference for a planetary mass/diameter/age model?

I was measuring from a rather lo-res graph in The New Solar System, 4th Edition.

But if you can read PS files, I'm sure more useful data can be retrieved from Tristan Guillot's homepage - he has done a lot of the theoretical work in this area.

Grant

[selden]

Thanks!

[MKruer]

Just a little update. i started a new thread in the Add-ons section
http://www.shatters.net/forum/viewtopic.php?p=15903#15903