Faster, smooth high precision orbits

[ajtribick]

I don't quite get what's being advocated here: is the intention that Charon-centric orbits will be hideous unclosed monstrosities, or some weird pseudo-Tychonian system, where Pluto orbits Charon, the Sun orbits Pluto and all the planets orbit the Sun?

[t00fri]

I don't quite get what's being advocated here: is the intention that Charon-centric orbits will be hideous unclosed monstrosities, or some weird pseudo-Tychonian system, where Pluto orbits Charon, the Sun orbits Pluto and all the planets orbit the Sun?

Come on, that's just Galilean "relativity". Nothing special at all. Implications of elementary Newtonian mechanics.

Did you never wonder how odd the orbits e.g. of Jupiter look from Earth? S&T: Jupiter is retrograding this month etc. Planetary orbits DO look odd if viewed in certain frames (like by an observer attached to Earth).

F.

[t00fri]

Here is a Theora AVI video sequence (Mplayer, VLC player http://www.videolan.org/) that illustrates the crazyness of the present orbits.

http://www.shatters.net/~t00fri/images/orbits.avi

When the Earth is transformed into its rest system, every child knows that the sun traces an orbit around it. Similarly the other planets evolve around the Earth on partially VERY complex orbits.

In Celestia the standard orbit lines (defined for the Solar rest frame) move around Earth as a whole and the Sun does not trace an orbit line at all....I certainly wouldn't call the presently drawn orbits "intuitive" in the Earth REST frame The present orbits are just not the orbits traced in the Earth REST system. They are simply incorrect in this frame.


F.

[ajtribick]

Thanks for not answering my question and lecturing me on Galilean relativity (which I knew already).

[t00fri]

Thanks for not answering my question and lecturing me on Galilean relativity (which I knew already).

Sorry your question wasn't exactly easy to understand

is the intention that Charon-centric orbits will be hideous unclosed monstrosities, or some weird pseudo-Tychonian system,

Your (boldfaced) expressions where unfortunately outside my scientific English ...

I didn't even understand what it had to do with the simple physical issue of drawing the correct orbits related to the reference frame under consideration. Good if you know already about the requirement of Galilei invariance. So why don't you tell us what you conclude from that?

I don't quite get what's being advocated here

What I advocate here is to apply the same Galilei transformation matrices that transform a planet to REST (for example) to all the orbit points as well. This will transform the whole orbit of that planet into one point (where it rests for all times ), while the orbits of the other bodies are transformed into the proper ones referring to the REST system of the particular planet.


Bye Fridger

[Chuft-Captain]

Sorry to cut into your thread guys, but as you're discussing reference frames (and you have Chris's attention ) I'd like to draw your attention to a possible bug in later pre-releases which I suspect is actually related to reference frames.
See here for details: http://celestiaproject.net/forum/viewtopic.php ... ght=#95630

Cheers
CC

Selden.
WOuld you prefer that I post this to the bugs thread instead.

[ElChristou]

I know that all this stuff as been studied for years and centuries, but for a neophyte it this questions, it's odd to see the term orbit used in any reference frame different than the parent's one... I mean it's odd to talk of the sun orbiting Earth for example because it's not the case and will never be... At best talking of a relative trajectory vis a vis a certain reference frame *seems* to be more appropriate...

Now one thing that would be great is to enable those relative trajectories (depending on the object selected) but keeping at the same time the "normal orbits" (the earth and others planets still orbit the sun even in Earth reference frame). The orbits could be dimmer (to be present but less than the relative trajectories), this to keep them visible as reference...

Sorry to "invent" terms, but was to illustrate the idea of having both representations in the same time...

[t00fri]

I know that all this stuff as been studied for years and centuries, but for a neophyte it this questions, it's odd to see the term orbit used in any reference frame different than the parent's one... I mean it's odd to talk of the sun orbiting Earth for example because it's not the case and will never be...

Christophe,

while Galilei relatiivity is still a "mild" form of relativity, Einsteins special and notably his general relativity are much much stronger versions, where the notion of "parent"=inertial systems and the like has lost it's meaning entirely.

In the present context, we are just talking about the fact that the laws of Newtonian mechanics (and astro mechanics) remain unchanged if we consistently transform ALL space-time points into another coordinate frame. An observer located on Earth is necessarily in a coordinate system where the Earth is at REST. If he observes the Sun in this coordinate system, indeed he sees it orbiting around Earth. I guess you have watched the Sun before? Seen from that geocentric coordinate system, the other planets perform partly very strange orbits.

Here is a WEB display that lets you get a feel e.g. for the little circles due to so-called retrograde movements most planets are some times performing at the sky, if watched from the Earth's REST system (geocentric system).

http://www.davidcolarusso.com/astro/

But we know (and use in Celestia) a well-defined set of matrices (quaternions,...) that lead us (i.e. transform us) e.g. from the Earth rest system to a system where the sun is at rest instead (heliocentric system). If you transform the planetary orbit points by the same matrices, you generate the appropriate orbits in the transformed system.

As you know well, these geocentric orbits have played an important role historically, until Copernicus and Kepler came along and told us that things get really simple (~elliptical orbits) in the REST system of the mother star. In case of multiple star systems these issues become quickly much less apparent and it is good that we know about Galilei relativity...

Now one thing that would be great, is to enable those relative trajectories (depending on the object selected) but keeping at the same time the "normal orbits" (the earth and others planets still orbit the sun even in Earth reference frame). The orbits could be dimmer (to be present but less than the relative trajectories), this to keep them visible as reference...

Sorry to "invent" terms, but was to illustrate the idea of having both representations in the same time...

I completely agree, as I indicated in my first reply above already. We should think about how to compute the various appropriate orbits quickly and accurately in different frames and how to display them in a most instructive manner.

Bye Fridger

[ElChristou]

Definitively it would be quite interesting to see those weird orbits...

[chris]

Also see this for some interesting trajectories viewed in various reference frames:

http://faculty.ifmo.ru/butikov/Projects ... tion2.html

--Chris

[t00fri]

Also see this for some interesting trajectories viewed in various reference frames:

http://faculty.ifmo.ru/butikov/Projects ... tion2.html

--Chris

BEAUTIFUL. Whoever needs still to be convinced about the possible diversity of orbits in different reference frames, have a look at this site! The others will just have fun with these great displays...

I liked particularly example 5 in the two displayed frames!

Thanks Chris!

Bye Fridger

[ElChristou]

Also see this for some interesting trajectories viewed in various reference frames:

http://faculty.ifmo.ru/butikov/Projects ... tion2.html

--Chris

I'm unable to contact this site...

[Cham]

Me too, I'm unable to see that page. I'm at my office right now, using that crappy %$#&* computer with its slow network connection in that %&(*@ college !

[t00fri]

The site is in Russia, but I don't have the slightest problems.

F.

[mjoubert]

We should think about how to compute the various appropriate orbits quickly and accurately in different frames and how to display them in a most instructive manner.

Useful enhancement for spacecraft ground coverage when earth reference frame is selected.

Mathieu

[mjoubert]

I'm unable to contact this site...

Same issue here:
"Erreur de chargement de la page", en fran?§ais dans le texte...

[t00fri]

I still say you're mad

Even my old friend thinks that Celestia is a bit "behind"



Cheers,
Fridger

[ElChristou]

H?©h?©... seems it's not the last time we will see this shot...

[t00fri]

H?©h?©... seems it's not the last time we will see this shot...

It's handy and my old friend is quite convincing

F.

[BobHegwood]

I still say you're mad

Even my old friend thinks that Celestia is a bit "behind"



Cheers,
Fridger

I'm afraid that I simply HAVE to agree with Dr. Schrempp here...

Hee, hee...