Pluto's orbit

[DonAVP]

I have a feeling that this has been discussed during development but I will toss it out there anyway. In 1.5 Pluto's orbit does not show up when the orbits are displayed in blue. I understand the reason because of its demotion as a planet. However I was over at Celestia Wikibook and was reading through some of the examples of how to us the program. In the one introducing the planets it makes mention of all 9 orbits. There are now only 8, unless you select the Pluto/Charon combo. A number of scripts and now this Wiki are slightly wrong and will need to be changed.
http://en.wikibooks.org/wiki/Celestia/Getting_Started#Introduction_to_using_Celestia

I propose that for now we turn on the Pluto/Charon orbit with the other planets so the older data will seem to make sense. As far as I am concerned the planet Pluto is still a planet and I would bet a dollar to a dozen donuts the public thinks the same. I would be more inclined to call them our only binary planets, just to be completely different.

Know let the wars begin 8^).

Don

PS I added edited some at the Wiki site and would encourage other to check it out and contribute your vast knowledge.

[selden]

Don,

A defect in Celestia causes the orbital paths of Reference Points not to be drawn. This is why you can't see the orbital path of the Pluto-Charon barycenter.

Celestia has not yet caught up with the formal changes in nomenclature. Hopefully both deficiencies will be fixed in the next version.

[duds26]

All that hasle about Pluto.
Just call it a planetiod.
There are a lot of big rocks having also a big path around the sun that are just called so.

[fsgregs]

Duds:

You can turn on Pluto's orbit by pressing the [9] key while orbits are selected. It will appear in red rather than blue, but at least it will be there.

Frank

[BobHegwood]

Duds:

You can turn on Pluto's orbit by pressing the [9] key while orbits are selected. It will appear in red rather than blue, but at least it will be there.

Frank

If you really wish to, you can also simply define Pluto the way it used
to be defined within the Solarsys.ssc file, and all of these strange
problems simply disappear. If you need to see the original
file, just download 1.4.1 and use the Pluto definitions created by
that setup.

Just FYI... Brain-Dead

[chris]

Duds:

You can turn on Pluto's orbit by pressing the [9] key while orbits are selected. It will appear in red rather than blue, but at least it will be there.

Frank

If you really wish to, you can also simply define Pluto the way it used
to be defined within the Solarsys.ssc file, and all of these strange
problems simply disappear. If you need to see the original
file, just download 1.4.1 and use the Pluto definitions created by
that setup.

This will result in Pluto's moons Nix and Hydra having the wrong orbits.

--Chris

[Nastytang]

Chris what part need`s to be change to show 9 orbits ???

[BobHegwood]

This will result in Pluto's moons Nix and Hydra having the wrong orbits.

--Chris

Can you not also modify their definitions in the appropriate ssc?

[chris]

This will result in Pluto's moons Nix and Hydra having the wrong orbits.

--Chris

Can you not also modify their definitions in the appropriate ssc?

Not really. The orbits are defined as ellipses, but they only remain elliptical relative to the Pluto-Charon barycenter. Right now, the hierarchy is:

Code: Select all

Sun +
    |
    +-- Pluto-Charon Barycenter --+
                                  |
                                  +-- Pluto
                                  +-- Charon
                                  +-- Hydra
                                  +-- Nix


You could redefine it this way:

Code: Select all

Sun +
    |
    +-- Pluto --+
                |
                +-- Pluto-Charon Barycenter --+
                                              |
                                              +-- Charon
                                              +-- Nix
                                              +-- Hydra


Then Pluto's orbit would show up because it's an immediate child of the Sun. You'd need to adjust the orbit of Pluto and Pluto-Charon Barycenter, but the orbits of the other objects could stay the same.

--Chris

[revent]

FYI, the pluto orbit in the Celestia distribution is pretty bogus anyhow. VSOP87 is based on DE200, and the DE200 Pluto orbit wasn't fit to observations.

[chris]

FYI, the pluto orbit in the Celestia distribution is pretty bogus anyhow. VSOP87 is based on DE200, and the DE200 Pluto orbit wasn't fit to observations.

VSOP87 doesn't include an orbit for Pluto, so we're using a different theory. It's still not very good, however. If you (or anyone) knows of a good orbital theory for Pluto, I'd appreciate some pointers.

For anyone who needs a more accurate orbit for Pluto, it is possible right now to replace the default orbit of Pluto with either the DE405/DE406 ephemeris or a SPICE kernel. I don't want to put huge ephemeris files into the default Celestia package, so I'd still like to find a good semi-analytic theory that improves on the current Pluto CustomOrbit.

--Chris

[chris]

As of SVN revision 4237, Celestia will show Pluto's orbit once again. It's actually the orbit of the Pluto-Charon barycenter, but it's colored like a planet orbit. I implemented a new rule for barycenter (reference point) orbits paths. For the purpose of orbit rendering, a barycenter is treated as if it were the same class as one of its child objects, with the following priority:

- Planet
- Moon
- Asteroid
- Spacecraft

Thus, if you create a binary asteroid with the orbits of its components defined relative to their barycenter, the heliocentric orbit of the barycenter will be shown and colored as if it were an asteroid orbit.

--Chris

[Cham]

Chris,

Pluto isn't a planet anymore, and its barycenter orbit shouldn't be shown as a planet. Obviously, it isn't an asteroid either. We need a new class for it, something like "plutonid", or "dwarf planet", or something else like that.

And what happens to the barycenter orbit if the children are defined as a planet and an asteroid, say (or any other combination) ?

[chris]

Chris,

Pluto isn't a planet anymore, and its barycenter orbit shouldn't be shown as a planet. Obviously, it isn't an asteroid either. We need a new class for it, something like "plutonid", or "dwarf planet", or something else like that.

I'll get around to adding a dwarf planet class eventually. But, I find this whole debate about categorization tiresome, so pardon my lack of enthusiasm.

And what happens to the barycenter orbit if the children are defined as a planet and an asteroid, say (or any other combination) ?

If the children have different classes, planet has priority, followed by moon, asteroid, and finally spacecraft. The classes are roughly ordered by significance, with the exception of spacecraft which doesn't really fit into the ordering. So planet wins out in the Pluto-Charon case. Planet also wins in a situation where a planet and spacecraft have orbits defined relative to the same barycenter.

--Chris

[Cham]

Chris,

I've just recompiled from SVN. Pluto's orbit is showing, but there's no label at all.

[chris]

Chris,

I've just recompiled from SVN. Pluto's orbit is showing, but there's no label at all.

I haven't changed labeling at all. Not sure what the best approach is . . . It seems reasonable to base the labeling on the orbit class and show 'Pluto-Charon' using the planet (or dwarf planet) color.

--Chris

[Cham]

Yes, "Pluto-Charon" should be shown with its orbit. Or else, it's really weird to have the barycentyer orbit showing (as a planet) without any label at all, while all other regular planets do have their label showing. Could be puzzling or looking like a strange bug to a novice.

[revent]

FYI, the pluto orbit in the Celestia distribution is pretty bogus anyhow. VSOP87 is based on DE200, and the DE200 Pluto orbit wasn't fit to observations.

VSOP87 doesn't include an orbit for Pluto, so we're using a different theory. It's still not very good, however. If you (or anyone) knows of a good orbital theory for Pluto, I'd appreciate some pointers.

For anyone who needs a more accurate orbit for Pluto, it is possible right now to replace the default orbit of Pluto with either the DE405/DE406 ephemeris or a SPICE kernel. I don't want to put huge ephemeris files into the default Celestia package, so I'd still like to find a good semi-analytic theory that improves on the current Pluto CustomOrbit.

Didn't know that VSOP87 didn't include a Pluto orbit. I'd assumed it did, and just noticed that the location of Pluto was way off.

I haven't tested it or anything, but http://www.moshier.net/ has a trig. series fit to DE404 for the planetary orbits (plan404.zip, about a quarter of the way down). He claims a fit to within 1 arcsec for Pluto.

[duds26]

This will result in Pluto's moons Nix and Hydra having the wrong orbits.

--Chris

Can you not also modify their definitions in the appropriate ssc?

Not really. The orbits are defined as ellipses, but they only remain elliptical relative to the Pluto-Charon barycenter. Right now, the hierarchy is:

Code: Select all

Sun +
    |
    +-- Pluto-Charon Barycenter --+
                                  |
                                  +-- Pluto
                                  +-- Charon
                                  +-- Hydra
                                  +-- Nix


You could redefine it this way:

Code: Select all

Sun +
    |
    +-- Pluto --+
                |
                +-- Pluto-Charon Barycenter --+
                                              |
                                              +-- Charon
                                              +-- Nix
                                              +-- Hydra


Then Pluto's orbit would show up because it's an immediate child of the Sun. You'd need to adjust the orbit of Pluto and Pluto-Charon Barycenter, but the orbits of the other objects could stay the same.

--Chris

Or the barycenter could be used to draw stuff, other problems with double planet's or planets with moons will disapear also (there is a discussion about saturns barycenter problem somewhere around in this forum and the moon and earth have also a barycenter but I think it's inside the earth so you can't notice it)