Our Suns wobble..

[xelasnave]

We all understand how they determine the existence of planets other than those within our solar system... they plot the "wobble" of a star and figure out what other bodies in that system causes such a "wobble".

AND so I wondered how much does our Sun wobble..does any one know?

I think our Sun must follow somewhat a spiral course thru space with it and the planets having a common center and have wondered where this "center" could be... does anyone understand what I am driving at and if so indicate where this center may be...
alex

[xelasnave]

OR put another way.. I feel the Sun can not be at dead center because it has to balance the planets and the "center" must be away from the Sun and that the Sun is not at the center exactly.
alex

[AGarvin]

Hi Alex,

I reckon the "centre" will still be within the Sun, just not in the centre of the Sun. My logic is that the centre of the Earth/Moon system is about 1400km below the surface of the Earth, and proportionally I would suspect that the mass/distance of that system is bigger than that of the Sun/planets.

Interesting question though.

Andrew.

[xelasnave]

If the "center" is below the surface of the Sun there must be a tidal effect that the planets make in the workings of the Sun one would expect..the planets may be the "spoon" that stirs the Sun. Maybe there is a link between that (if a fact) and Sun spots maybe???

If the center is outside the Sun there would be a vortex effect originating from that region one would think.

I wonder about binary star systems and conclude they must orbit a center that has moved on (assuming gravity travels at a finite speed which I think could be the only way it could be..instant sounds fine but that could not be..instant means something moves from one end of the Universe to the other in er an instant..impossible and contrary to GR I expect)

Anyways the effect of following a moving center must produce a vortex effect...er it would if gravity pushes and if not via push some major effect must be evident.
alex

[Jazza (Jay)]

Binary systems do indeed orbit a center of gravity.
Similarly so do solar systems, no idea where it is for ours!
However binary pulsars (that is a system with two pulsars orbiting each other) are an excellent test of GR as they emit very stable pules of radiation at a set timing. This shows that indeed gravity does not act instantaneously but at the speed of light
Jay

[astroron (Ron)]

The Sun does wobble, and the Centre of mass of the Solar System is not in the centre of the sun but at a point away some distance it.
The Planets Jupiter and Saturn have an effect on the Sun more so when they are both on the same side as each other.
There is an hypothasis that the Sun has a companion, by the way which I believe in.
Here is a site that you might get some info on your question.

http://www.binaryresearchinstitute.org/index.shtml

I hope this helps
Ron

[xelasnave]

Thank you Jay and Thank you Ron.

My point with the center thing is that as gravity has a finite speed each object will "aim" for a position where the other has left.I think that this in effect provide two centers ...and these two centers will scribe a vortex pattern...I first considered the speed of gravity when I asked myself why a comet does not hit the Sun..if you think about it given that it starts some 2 to 3 light years out one would wonder why it could not line up the Sun.. drop a stone on the Earth and it does not miss...well of course where the comet thinks the Sun is when it starts it journey was in fact a place where the Sun was...some 2 to 3 years ago..and so it heads off to that point continually correcting but its only hope of a hit would be to "lead" the Sun by aiming ahead of it (ahead of where the message of gravity has suggested it to be...

in fact I feel that it is this situation that may well power orbits in binary systems..(even our Solar system) just an idea but one which I can not express very well so as to sound more than nonsence. You need to see my hands move to understand me most times or give me chalk and a blank wall.

Well if the center between the Sun and the planets is above the surface of the Sun I predicte that in that region there should be a vortex which may well eject matter moving into it.... I think that binaries should have a vortex generated by the rotation of in effect two "centers".

Anyways thanks very much guys I will read up at that link and all the other links that link will no doubt link to.

alex

[bojan]

Lets put some math to this discussion....
The mass of the Sun is known, the mass of the Jupiter and planets are known... it is not that hard to calculate the position of the centre of mass of the solar system, so that we can move away from "feelings" in discussions like this one.... Numbers, numbers....
BTW, it is not the change of the star position, but the change of the star radial speed that reveals the presence of extrasolar planets.
The current detectability is ~1m/s only... still not enough to detect the presence of Earth-size planet at the right distance orbiting around solar-size star..

[xelasnave]

So Bojan what math should we use?? the math as to levers is as complex as I can get ..will that do it?? I still have not turned up anything on this.
alex

[Zuts]

Originally Posted by xelasnave

So Bojan what math should we use?? the math as to levers is as complex as I can get ..will that do it?? I still have not turned up anything on this.
alex

http://en.wikipedia.org/wiki/Center_of_mass

Paul

[xelasnave]

Thank you very much for that Paul.

alex

[bojan]

Originally Posted by xelasnave

So Bojan what math should we use?? the math as to levers is as complex as I can get ..will that do it?? I still have not turned up anything on this.
alex

Yep, lever math will do here.. However Paul's link to Wikipedia is very good.
Actually, whenever I need more than just trivial explanations, or when I want to remind myself of things I used to know a loooooong time ago, I go to Wiki...
One of the best sources of knowledge available today.. except for the "hot" stuff.... it gets "edited" and edited a bit too often

[xelasnave]

I like Wiki as for me I can wander off on the links and from those links to others..and the good thing is most well everthing is new..even stuff I knew once presents that way.... I wish I had it when I was a kid..the only reason I was good at chemistry in the early days was becasue those were the only books I had .. a relation who went to Uni had them so I read them when we visited ... kids are very fortunate today to be able to source anything how wonderful for an enquiring mind.

alex

Those sums did not take into account time..I just realised so I will have another look..but you need time when on the scale of the solar system because messages take long times to get where they are going... this is why I say there must exist in effect different "centers"everything will think they orbit a common center but if you stood back they must all orbit where they think other objects are..hence time is an ingredient... evn doing it via a lever you wouold have to look at it that way...

anyways I am looking at it all again today ... any math experience must be good for me.

alex

[bojan]

Alex, there is no need to account for time (you probably meant gravity propagation?) in to those calculations, because the effects would have been very, very small anyway in cases like multiple star and planetary systems (non-relativistic.. and even when extreme cases are considered, not taking time into the picture is a good first approximation)

[xelasnave]

Well I am a little focused on the aspect of the propogation of gravity Bojan and the inevitable conclusion it is not instant.. and a belief that even on small scales this aspect that centers are "different" for each object and that it is this difference that in effect "powers" the rotation of a binary system ..for example.. I can make a case but it is something that I alone am probably interested in.
Thanks for you help I really appreciate it.
alex

[bojan]

Originally Posted by xelasnave

Well I am a little focused on the aspect of the propogation of gravity Bojan and the inevitable conclusion it is not instant.. and a belief that even on small scales this aspect that centers are "different" for each object and that it is this difference that in effect "powers" the rotation of a binary system ..for example.. I can make a case but it is something that I alone am probably interested in.
Thanks for you help I really appreciate it.
alex

Personally, I would never assume I am the only person in the world that worries about this and that.. So this aspect of gravity was addressed before, I am sure (but I can not tell you by whom and when at the moment..).
However, when you are in some problem more deeply (by this I mean understanding the math involved) , then you will know if something is relevant or not.
And in case of binary systems, the time is not important in the way you are trying to imply... Yes, the gravity propagates by the speed of light, but this propagation time is so short compared to other time frames that you can comfortably put those effects aside as the first approximation.. possibly even as the second and the third:-) .

[bojan]

What you are probably worried about is illustrated in the following example:

Lets have a close binary system, orbited, by the third component say 10x further, and them 4th component, again 10x further.
But, the gravity centre for the first pair is calculated by simple "lever" math.. Then you use this Centre (which is now a single spot in space with combined mass of two components), and calculate the nex tcentre of mass with the 3rd component.. and so on.
No need for time here.
The time is needed to take into consideration only in relativistic cases, where gravity waves are emitted and where, indeed things are not simple.. But Dr A, took care of this :-)

[xelasnave]

I dont even know the range of distances for binaries orbital distances Bojan.. so approximation is my main tool.

However I can not see that the two center thing can be erroneous... and although relatively insignificant I feel this aspect will be relevant in the paths of each individual star in the system...

I dont know if a distance of one light year is unreasonable but for the sake of making the point I find so captivating I will go with that...

if we have two stars one light year distant to each other in orbit and say they travell at the speed of our Sun..which I believe to be some 350 klms per second by the time the message of gravity arrives each star has moved on by some 350 x 60 x 60 x 24 x 365 klms... see I try and use math I am not sure but this suggest that the center will be off by that number divied by two (maybe)... anyways it will be considerable...each star relates to a position the other has moved well past...

anyways I take your point as to approximations.. I do it all the time because I have no alternative... but as to centers I feel an approximation wont show the point I am working up.. but I see this difference in centers as perhaps responsible for the "power" to run the orbit... it certainly adds up in a push environment for me

I hope you are right about others having somewhat similar thoughts..being alone with the only human conversation I have limited to this and one other forum I tend to feel a little ..er alone.

You may find this hard to believe but when I meet folk in the real world they dont seem to care much for any thing relating to astronomy or gravity and so I feel that I am a late developing nerd..which I am very happy with for myself.

Thanks again for your kindness
alex

[bojan]

In a typical binary system,stars are from light-hours to light-days apart.
Alpha Centauri:
A & B are couple of hours apart and the orbital time is ~80 years.
Proxima is 13 light-days away, orbital period in excess of 100.000 years.
You can use Kepler'd laws here they apply perfectly, to verify the consistency of those numbers.
So you can see, the gravity propagation is irrelevant.
What is not relevant is the influence of components A & B to eventual planets in a stable orbits around them.
Or, in our case, Sun-Jupiter system, and inner planets (the influence of Jupiter and other bigger planets to smaller ones and vice versa is called "perturbations" and this influence is fully accounted for... otherwise we would not be able to calculate the planets positions couple of thousands of years in the past and in the future. (Even the light pressure from the Sun's illumination is taken care of in attempt to precisely calculate the orbits and positions of asteroids..))
This is called "n-body" problem.
Again, no need to take gravity propagation into account. Have a look at wiki.
Also have a look at any celestial mechanics book (Meeus perhaps?)

[Zuts]

Gravity travels at a finite speed, the speed of light. In a binary system the companion star did not appear out of nothing, the mass has been there for ever.

The equations in Wikipedia are for the 'instananeous' case. The equation must be summed over all pairs in the system; they give the answer at a particular D for a particular pair at a particular time.

To be more correct you could replace the D with a function containing T time.

As the bodies orbit each other the center of mass for a n body system will change at the speed of light.

Also you cant really check this because your communication of the measurement if you could actually make it would also be limited to the speed of light.