Orbital trails?

[Evil Dr Ganymede]

Is it possible to add 'orbit trails' to Celestia?

Obviously, one can see an object's orbit as the blue/red ellipses. But say I'm looking at a binary star system, which has a planet orbiting the pair in a distant orbit. I go above the system, so I can see all the bodies (and turn on the orbits), lock the view to a star, and speed up time.

The path that the planet takes around the stars won't be circular, it'll be all loopy because you're looking at it in a rotating reference frame. But as it stands, I can't see the path it takes, because the orbits remain elliptical.

I presume there isn't a way to change how the orbits are drawn depending on the reference frame. But is there a way to perhaps make a 'trail' behind the object, or maybe a timelapse movie of its path? The only way I can think of is to regularly save the view as an image and put that together in photoshop, but that's really arduous. Ideally, I'd prefer something that can be done in Celestia, but if it's possible to make a timelapse movie of the object's location then that'd be OK. I guess it could be done by adding an option to make a movie but to keep all the previous frames visible in the animation instead of overwriting them?

Or is there any other way to do this?

[selden]

Or is there any other way to do this?

Sure.

Just define lots more objects that follow along behind the object of interest.

To first approximation, their SSC entries would be identical to that of the object you're interested in, except that their Mean Anomaly values would be ever so slightly progressively smaller. Maybe give each object a progressively smaller Radius, too.

[Evil Dr Ganymede]

Or is there any other way to do this?

Sure.

Just define lots more objects that follow along behind the object of interest.

Cunning, but I don't think that's quite what I'm after.

That just makes a trail of objects that follows the planet on its blue orbit line - but that's still an ellipse. I've got objects spaced every 10 degrees in the orbit like you suggest, but I can't see any kind of 'flower petal' pattern when I speed it up.

Unless I'm misunderstanding what you say? I'm doing it like this (viewing from 10AU above the orbital plane):

Code: Select all

# Data for our binary system.

"Star1" "HIP 400000"
{
Texture "gstar.jpg"
Radius 696265

Emissive true

EllipticalOrbit {
Period 0.33
SemiMajorAxis 0.300
Eccentricity 0.0
Inclination 0.0
AscendingNode 0.0
LongOfPericenter 0.0
MeanAnomaly 0.0
}
}

"Star2" "HIP 400000"
{
Texture "kstar.jpg"
Radius 696265

Emissive true

EllipticalOrbit {
Period 0.33
SemiMajorAxis 0.300
Eccentricity 0.0
Inclination 0.0
AscendingNode 0.0
LongOfPericenter 0.0
MeanAnomaly 180.0
}
}

"Planet" "HIP 400000"
{
Texture "earth.png"
Radius 5000000

EllipticalOrbit {
Period 1.85
SemiMajorAxis 1.900
Eccentricity 0.00
Inclination 0.00
AscendingNode 0.0
LongOfPericenter 0.0
MeanAnomaly 0.0
}

Albedo 0.30
}




"p2" "HIP 400000"
{
Texture ""
Radius 5000000

EllipticalOrbit {
Period 1.85
SemiMajorAxis 1.900
Eccentricity 0.00
Inclination 0.00
AscendingNode 0.0
LongOfPericenter 0.0
MeanAnomaly 10.0
}

Albedo 0.30
}


"p2" "HIP 400000"
{
Texture ""
Radius 5000000

EllipticalOrbit {
Period 1.85
SemiMajorAxis 1.900
Eccentricity 0.00
Inclination 0.00
AscendingNode 0.0
LongOfPericenter 0.0
MeanAnomaly 20.0
}

Albedo 0.30
}

"p2" "HIP 400000"
{
Texture ""
Radius 5000000

EllipticalOrbit {
Period 1.85
SemiMajorAxis 1.900
Eccentricity 0.00
Inclination 0.00
AscendingNode 0.0
LongOfPericenter 0.0
MeanAnomaly 30.0
}


[selden]

You understood me, but I wasn't thinking clearly. I'm probably still not.

What you want to see is where the object was at some time in the past. Just changing the MeanAnomaly doesn't do that: it shows a planet now that's in the same current orbit. Hmmm.

I'm afraid I can only think of the same thing you did, although I'd probably use a slightly different technique: have Celestia make a movie from the desired viewpoint and use a scripting language to add all of its frames together.

I'd probably use bash plus NetPBM or ImageMagick to split the movie and add the frames, but it comes down to the same thing.



Sorry.

[Evil Dr Ganymede]

Figured as much
Oh well, thanks anyway.

Happy new year!