Charon moves opposite direction to the other Pluto moons

[Ajaja]

Charon moves the opposite orbit way around Pluto.
Positions of Nix, Hydra, Kerberos and Styx are far away from real too (I did some checks using Horizons here https://gist.github.com/Ajaja/02f67dc19d567f771f260d2939ba9ec8 ) but al least they move in right direction.

System

• Stellarium version: 23.1

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[gzotti]

Can you provide better orbital elements? In any case, Pluto and Charon have bound rotation.
For the others: sure. Just use updated elements. Where can we find them?

[Ajaja]

@gzotti
I think Horizons System can provide necessary data.
Anyway, it's easy to see in ssystem_major.ini that Charon has positive orbit_Period and small orbit_Inclination, all other Pluto moons have negative orbit_Period and small orbit_Inclination too. So, they definitely move opposite ways in Stellarium.
In the reality they move the same way.

[gzotti]

Fine. Where do we find elements?

[Ajaja]

On Horizons System, as I said. For any epoch.
For example:
https://ssd.jpl.nasa.gov/api/horizons.api?format=text&MAKE_EPHEM=YES&COMMAND=901&EPHEM_TYPE=ELEMENTS&CENTER=%27500@999%27&START_TIME=%272023-05-25%27&STOP_TIME=%272023-05-26%27&STEP_SIZE=%271%20DAYS%27&REF_SYSTEM=%27ICRF%27&REF_PLANE=%27BODY%27

Previously I made a mistake in a sign in https://gist.github.com/Ajaja/02f67dc19d567f771f260d2939ba9ec8
Now I fixed it. Looks like after all Charon moves in the right direction, but all other Pluto moons move in Stellarium in the wrong direction.

[Ajaja]

It's easy to get elements for any specific date: https://gist.github.com/Ajaja/b438bf50a2c21d4496f67c30c20c8871
Maybe, a better approach would be to calculate average elements for some reasonable period.
Anyway, Kepler orbits won't be working well for long periods with Pluto-Charon system, especially for small moons, but at least correct ones for some epoch will fix direction of orbital movement.

[gzotti]

You can work out changes required in ssystem_major.ini and send a pull request. Indeed, elements in Horizon show a change, so any static solution is temporary only. If there is a model published for the non-Keplerian solution of Pluto's moons, we could also implement that. However, it is a problem that rarely causes me headaches. Most people have difficulties observing Pluto, let alone Charon, or even the smaller pebbles. For now we could just invert the motion of the smaller ones as qualitative fix.

[github-actions]

Hello @Ajaja!

Please check the fresh version (development snapshot) of Stellarium:
https://github.com/Stellarium/stellarium-data/releases/tag/weekly-snapshot

[github-actions]

Hello @Ajaja!

Please check the latest stable version of Stellarium:
https://github.com/Stellarium/stellarium/releases/latest