True (orbiting) binary stars in .ssc files possible?

[Medusa]

Hi folks,

maybe I've not found yet the right of the FAQs for this, so bear with me...

I want to add some multiple stars like Algol, Castor, Sirius with the true orbital elements of the companion stars. (Some of them orbit faster than some known planets.)
How is it possible? The "Class" entry in a .ssc file does not have "star", and .stc files define only single stars without orbital motion (is that correct?).

Thanks for your help,

~Medusa (Diane).

[selden]

Celestia does not yet have the ability to display multiple-star systems properly. Mutual orbits and multiple light sources are not yet supported. There is reason to hope that these features will be available in the next release of Celestia, but it isn't clear when that might be ready.

In the meantime, a workaround is to declare the "minor" members of the system as planets and specify

Emissive true

so that those planets seem to glow.

You might want to take a look at http://www.lepp.cornell.edu/~seb/celestia/hutchison/spreadsheets.html#2
where Grant Hutchison has provided a spreadsheet to calculate appropriate orbital parameters.

[chris]

I'm working on multiple star systems right now, and just completed the first stage of development last night. The emissive planet approach that Selden mentioned is the right thing to do for now, but soon you'll be able to create 'real' multiple star systems.

--Chris

[Medusa]

Hi folks,

ok, thanks for your rapid answer(s). I already tried the "Emissive true" trick for Sirius B, but it's really just a preliminary solution. For Sirius B, a white dwarf it might be ok, and some additional cosmetics can be done by an extended "Atmosphere".

But what I really had in mind were close eclipsing binaries, contact or semicontact systems like Algol or Epsilon Lyrae. Moreover, such binary stars are not spheres but quite deformed by gravitational forces. Maybe another idea for Chris for future versions of Celestia...?

Greetinx, ~Medusa.

[buggs_moran]

Chris,

Real multiple star systems with orbital motion and no proper motion, right? Most of our computers probably couldn't handle proper motion as well as all of the other (AWESOME) features. I can't wait! Showing my students the difference between eclipsing/spectral/visual binaries will be great (dreaming of Epsilon Lyrae ). Your program is an incredible teaching tool.

Buggs

[Medusa]

Hi,

silly I am, it was BETA Lyrae I wanted to talk about, not Epsilon. But as I saw from your reply, you nevertheless got my point... *dreaming of it, too*...

~Medusa.

[Evil Dr Ganymede]

Contact binaries/ellipsoidal stars would be a nifty addition (even if you could just specify an oblateness for stars manually)... but let's just let Chris sort out the basic binary star support first though

[granthutchison]

Contact binaries/ellipsoidal stars would be a nifty addition (even if you could just specify an oblateness for stars manually)... but let's just let Chris sort out the basic binary star support first though ;)

The plan is to eventually allow mesh objects to be specified for stars. Once that happens, I'll aim to produce a selection of true Roche-lobe shaped objects that can be used in stc's.

Grant

[chris]

Contact binaries/ellipsoidal stars would be a nifty addition (even if you could just specify an oblateness for stars manually)... but let's just let Chris sort out the basic binary star support first though

The plan is to eventually allow mesh objects to be specified for stars. Once that happens, I'll aim to produce a selection of true Roche-lobe shaped objects that can be used in stc's.

In the CVS version, it's already possible to provide a custom mesh for stars. Oblateness will be working by tonight, and hopefully general ellipsoids as well.

--Chris

[Medusa]

That's what I thought how I would suggest it. I will *love* to see it work. You are doing an exceptional fine job with Celestia. Do you know you make some of my youth dreams come true?
I'll put an asteroid "Diane's Dreams" in an orbit around Beta Lyrae....

Thanks a lot, Chris,

~Diane.

[Evil Dr Ganymede]

Contact binaries/ellipsoidal stars would be a nifty addition (even if you could just specify an oblateness for stars manually)... but let's just let Chris sort out the basic binary star support first though

The plan is to eventually allow mesh objects to be specified for stars. Once that happens, I'll aim to produce a selection of true Roche-lobe shaped objects that can be used in stc's.

Grant

But presumably the program won't be able to calculate the shape of the stars on the fly though (since it doesn't care about the mass of the stars)?

To be honest, I find the absence of a mass parameter in Celestia to be rather frustrating, especially when I'm building systems - I'd love to just be able to enter either an orbital period or a semimajor axis and have Celestia calculate the other parameter of the pair using the mass of the primary. Just because a mass parameter is there doesn't mean that Celestia has to incorporate gravity's effects on objects - it could just be used to help calculate things like this.