[SOLVED] Pluto Orbit Confusion

[extremecrew]

This is more of a visual annoyance more than anything, but I believe this a bug: When selecting Pluto in a SVN-compiled Celestia, revision 4446 (with orbits turned on for planets, dwarf planets, and moons), it seems to be selecting a small circular orbit rather than the main orbit that is shown. Is there a quick fix to this in one of the orbit configurations, or is it something I'm missing?
A screenshot is attached.

[John Van Vliet]

--- edit ---

[ElChristou]

I see nothing wrong in the shot; Pluto's orbit is the small red one and the blue one is the orbit of Pluto-Charon barycenter...

[chris]

This is more of a visual annoyance more than anything, but I believe this a bug: When selecting Pluto in a SVN-compiled Celestia, revision 4446 (with orbits turned on for planets, dwarf planets, and moons), it seems to be selecting a small circular orbit rather than the main orbit that is shown. Is there a quick fix to this in one of the orbit configurations, or is it something I'm missing?
A screenshot is attached.

ElChristou is correct: there is no bug here. What's going on is this: Charon is so massive relative to Pluto that the two objects orbit a common point located far from Pluto's center--so far from Pluto's center that it actually lies outside of Pluto. This point is called the barycenter. The small circle is Pluto's orbit about the barycenter. What you've called the main orbit is actually the orbit of the Pluto-Charon barycenter around the Sun.

--Chris

[extremecrew]

That makes sense! Thanks for the quick replies.

[John Van Vliet]

--- edit ---

[Reiko]

I have a question about this. I've made double planets similar to the pluto/charon arrangement but can never get the orbit of the barycenter around the star to show up.
What could I be doing wrong that won't let it show up?
In fact, the pluto/charon barycenter doesn't show up either.

[Reiko]

How do you get the orbit for the pluto-charon barycenter to show up?
I have the orbits for planets and dwarf planets turned on but it still doesn't show.



Even when i select the pluto-charon barycenter the orbit still doesn't appear.



Is their a trick I don't know about?

[chris]

Is their a trick I don't know about?

This should be working automatically in the latest SVN versions (any build from the last couple months.) What Celestia version are you using?

--Chris

[Reiko]

Is their a trick I don't know about?

This should be working automatically in the latest SVN versions (any build from the last couple months.) What Celestia version are you using?

--Chris

It's fixed now. The problem was the old SSC file I was using didn't have these lines in it.
Visible true
Clickable true

[dahemac]

This is an actual problem with the data, not a misunderstanding.
This is a view of the solar system in Celestia 1-4-1 showing Pluto's orbit around the sun.


This is the same Favorite in Celestia 1-5-1.


This is a closeup of Pluto in the same general view as the image above. No moon orbits are shown the blue line is mistakenly the orbit of pluto around the sun.


That this is the orbit of Pluto around Sol is proven as I toggle planet orbits off.


I am by no means any kind of data expert, however I think the SSC file calls the same data for the solar orbit as the pluto lunar system orbits.
OrbitFrame {
EquatorJ2000 { Center "Sol/Pluto-Charon" }
}

BodyFrame {
EclipticJ2000 { Center "Sol/Pluto-Charon" }

[ElChristou]

...This is a closeup of Pluto in the same general view as the image above. No moon orbits are shown the blue line is mistakenly the orbit of pluto around the sun...

... To me this is Puto's orbit around it's barycenter...

[dahemac]

It is supposed to be the orbit around the Sun. What I am saying is that the data file for the solar system "solarsys.ssc" is somehow in error. It will not show Pluto's orbit around the sun correctly. Instead it shows Pluto's orbit around its barycenter. The following is the data in V1-5-1, then the data from V1-4-1. V1-4-1 shows the orbit correctly.

OrbitFrame {
EquatorJ2000 { Center "Sol/Pluto-Charon" }
}

BodyFrame {
EclipticJ2000 { Center "Sol/Pluto-Charon" }
}

EllipticalOrbit
{
Epoch 2452600.5 # 2002 Nov 22
Period 6.387206 # mean
SemiMajorAxis 2043.1 # mass ratio of 0.1166
Eccentricity 0.003484 # mean
Inclination 96.1680 # mean
AscendingNode 223.0539 # mean
ArgOfPericenter 337.92 # mean
MeanLongitude 77.960

CustomOrbit "pluto"
EllipticalOrbit
{
Period 248.54
SemiMajorAxis 39.48168677
Eccentricity 0.24880766
Inclination 17.14175
AscendingNode 110.30347
LongOfPericenter 224.06776
MeanLongitude 238.92881
}

[ElChristou]

It is supposed to be the orbit around the Sun. What I am saying is that the data file for the solar system "solarsys.ssc" is somehow in error. It will not show Pluto's orbit around the sun correctly. Instead it shows Pluto's orbit around its barycenter. The following is the data in V1-5-1, then the data from V1-4-1. V1-4-1 shows the orbit correctly...

But as both versions have nothing to do one with the other (there was no barycenter in 1.4) what's the point to compare them?
You should not lose your time, just download a fresh 1.6 and at best you will find back what you are looking for...

[selden]

Pluto does not orbit around the Sun.
Pluto orbits around the barycenter of the Pluto-Charon system.

Most of the binary objects in the solar system consist of bodies with very different masses (like the Earth and its Moon) so that their barycenters are somewhere deep inside the larger of them. As a result, it is reasonable to consider them as consisting of a large body orbiting the sun and a small body orbiting the large one.

This is not the case for Pluto and Charon. Charon is so massive compared to Pluto that the barycenter of the two of them is far above Pluto's surface, causing Pluto to travel in an ellipse around it. Their barycenter is what orbits around the Sun.

The orbital path of the Pluto-Charon barycenter is not drawn properly in Celestia v1.5.1. That problem is fixed in v1.6, so that it looks more like what you're used to seeing.

[dahemac]

The point is that the data in the solarsys.ssc for the current version 1-5-1 doesn't seem to allow Celestia to show Pluto's orbit around the sun. It shows Pluto's orbit around its barycenter instead. The solarsys.ssc data files from v1-4-1 and v1-5-1 have identical orbital data for other planets like Mercury, but different data for Pluto. I did a test and pasted the Solar orbit data from the v1-4-1 solarsys.ssc into the v1-5-1 solarsys.ssc and Pluto's orbit appeared. It was off centre somehow because I do not really understand the data. However this seems to show that the data for that orbit is missing from the v1-5-1 solarsys.ssc. v1-6 has not been released as far as I can tell.

[selden]

As we keep telling you, it is a bug in Celestia v1.5.1 which is fixed in v1.6.

[ElChristou]

...because I do not really understand the data.

That may be the problem... Listen to good old Selden... 1.4 and 1.5 are history. Go grab a 1.6...

[dahemac]

I understand that now. And assume that there is nothing I could change in the "solarsys.ssc" file to fix it. Thanks.
I use Celestia to visualize illustrations I am doing. I just used v1-4-1 to get what I needed.

Is version 1-6 available for Mac OS? If not, do you have any idea when it may come out?

[ElChristou]

I understand that now. And assume that there is nothing I could change in the "solarsys.ssc" file to fix it. Thanks.
I use Celestia to visualize illustrations I am doing. I just used v1-4-1 to get what I needed.

Is version 1-6 available for Mac OS? If not, do you have any idea when it may come out?

Do a search, someone ask this a while ago and you should be able to find the thread easily.