# Solar system motions

## Main Question or Discussion Point

This thread has been split off from the [thread=104694]Gravity Probe B[/thread] thread. Some posts here are duplicated in the above thread to keep a sense of continuity -- cristo

The "solar system’s change in angular velocity relative to the guide star" will be caused by its motion around the galaxy, I have dealt with the motion of the galaxy itself above (it is negligible).

Orbiting the galaxy would cause a geodetic precession of

$$(\frac{M_G}{M_E})^\frac{3}{2}(\frac{R_E}{R_G})^\frac{5}{2} \times 8 \text{arcsecs/yr }$$

(See MTW 'Gravitation' page 1119 eq 40.35)

i.e. about 10-8 arcsecs per year.

I think this can also be safely ignored!

Garth
Yes, but aren't you being dogmatic? Polestar101 is suggesting that the solar system is not orbiting the galaxy (at least, not only) but a binary companion(or something else, I would say). In that case the change in angular velocities(and in so called geodetic precession) will be greater than the one caused by the orbit around the galaxy.

There's some evidence for this. See the "http://en.wikipedia.org/wiki/Solar_apex" [Broken]" entry on Wikipedia.

I've also found out a paper from circa 1880,
"On the Movement of the Solar System in Space, deduced from the Proper Motions of 1167 Stars"
That paper is clearly pointing to a movement that is NOT the movement around the galaxy, but a movement with a far greater amount of change.

Please note also that the literature tends to differentiate between the movement of the Local Standard of Rest (LSR), which is the assumed movement around the galaxy, of the solar system and its local surroundings, and the proper movement of the solar system towards the solar apex.

I don't understand why these movements of the Solar system towards the so called solar apex, which are being studied since at least the nineteen century, are unknown or are not taken into account. Why these issues were forgotten or ignored in the course of time? Maybe because there's no known mechanism to explain them?

Regards,
Mauro

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Yes, but aren't you being dogmatic? Polestar101 is suggesting that the solar system is not orbiting the galaxy (at least, not only) but a binary companion(or something else, I would say). In that case the change in angular velocities(and in so called geodetic precession) will be greater than the one caused by the orbit around the galaxy.
Hi Mauro

Garth is correct based on the prevailing assumptions – but you are correct that if those assumptions are not accurate then the angular velocity of the solar system could be much higher. This was the gist of a poster/paper on “Earth Orientation” that I presented in the Geodesy group at the recent AGU conference in SF.

We measure changes in earth orientation to VLBI reference points far outside the solar system yet we do not account for any motion of the solar system frame relative to those reference points. In fact because we allocate all changes in earth orientation to local dynamics (traditional lunisolar inputs) we effectively constrain solar system motion to zero. So the big question is how much angular velocity is contained within the total annual precession observable of about 50.3” p/y.

The best way to solve this problem in my opinion is to try to measure how much the earth actually precesses relative to objects within the moving frame of the solar system (i.e. EO changes relative to the moon, the sun, Venus, etc.) then compare these amounts to the EO measurements taken relative to VLBI reference points outside the moving frame.

The result we find is nutation and Chandler wobble and other short period effects are locally measurable and therefore appear to be directly traceable to local dynamics, whereas precession is nowhere to be found when measuring relative to local objects. In other words, we only see precession when measuring relative to objects outside the moving solar system indicating that what we call precession is largely just the angular velocity of the solar system relative to reference points outside the moving frame.

Incidentally, thanks for the old article on solar system motion. There have been a few other similar articles over the years, and even the IAU in 2006 said the current precession nutation model was “inconsistent with dynamical theory” (IAU P03). Alas, until we start traveling out of the solar system I doubt anyone will seriously question assumptions about its motion.

Yes, but aren't you being dogmatic? Polestar101 is suggesting that the solar system is not orbiting the galaxy (at least, not only) but a binary companion(or something else, I would say). In that case the change in angular velocities(and in so called geodetic precession) will be greater than the one caused by the orbit around the galaxy.
Yes, and what he doesn't get (and which I don't have the patience to explain to him) is that all of the motions that he thinks he will see are ones that have long ago been excluded. Since you seem to be rational, I'll explain to you why his ideas (and I don't know of a nice way of saying this) are totally nutty.

One problem is that the earth's wobble is such a well known and obvious effect that astronomers correct all of their measurements for it, and he is looking in journals and not seeing precession because when numbers are quoted precession is removed. It's something that they teach you to do in freshman astronomy classes. Polestar doesn't under very, very basic astronomy. I don't have the patience to teach him, and he doesn't seem to be interested in learning.

There's some evidence for this. See the "http://en.wikipedia.org/wiki/Solar_apex" [Broken]" entry on Wikipedia.
That paper is clearly pointing to a movement that is NOT the movement around the galaxy, but a movement with a far greater amount of change.
This is well known motion. Basically if you look at the stars, you get an effect that looks a lot like what the stars look like when Han Solo goes into warp drive. This is largely irrelevant for the purposes of the gravity experiment, because the sun to the first approximation is moving in a straight line through the stars. The only effect would be if the movement of the sun is curved, and that's a small effect.

I don't understand why these movements of the Solar system towards the so called solar apex, which are being studied since at least the nineteen century, are unknown or are not taken into account.
They don't matter for the purposes of this experiment, because as long as the sun is moving in a straight line, it's not accelerating and if it's not accelerating then they don't effect any experiments designed to measure acceleration.

One way of thinking about it is to imagine Captain Kirk on the Starship Enterprise. When the Enterprise is going through the star field, you see star move past, but Kirk isn't getting bumped around. It's only when the Enterprise makes a sharp left turn that Kirk gets thrown around the bridge of the Enterprise. Now imagine a spinning gyroscope on the bridge, and you'll see why the local movement of the sun doesn't matter.

Why these issues were forgotten or ignored in the course of time? Maybe because there's no known mechanism to explain them?
All of these mechanism are not forgotten and they are well known, and people do take them into account.

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Also there are very strong limits on the existence of any extra solar star based on

1) celestial mechanics. Anything that could simulate axis precession would wreck havoc on solar system planetary motion

2) comets. Something with a 26,000 year orbit would be in the Oort and Kupier belts and we'd see comets raining down from that area

3) stellar evolution. Any star that is within a 26,000 year orbit is going to be seen.

This is just a totally nutty idea. There's a whole literature that places on the extra-solar system objects which are possible. Planet X and Nemesis. It's just one step above flat earth.

One problem is that most of the people on this thread are GR experts, and if you want to rule out the existence of a binary companion to the Sun, the strongest tests are not GR effects.

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They don't matter for the purposes of this experiment, because as long as the sun is moving in a straight line, it's not accelerating and if it's not accelerating then they don't effect any experiments designed to measure acceleration.
Just for clarity: the Sun is not moving in a straight line. It is moving in what we consider to be, in the relative short term, equivalent to a straight line.

All of these mechanism are not forgotten and they are well known, and people do take them into account.
So, can I ask you what is the presumed cause of these movements?
And what's the known rate of curvature and/or acceleration of the movement towards the solar apex?
Or, in other words, assuming this movement is elliptical, o equivalent to an elliptical movement, what is its period in years?

Thanks,
Mauro

Also there are very strong limits on the existence of any extra solar star based on

1) celestial mechanics. Anything that could simulate axis precession would wreck havoc on solar system planetary motion
This a strong objection, and it's the main reason I disagree with Polestar101. If the solar system is moving in a curved path, that movement will produce parallax effects, not precession. The only way for them to produce precession, would be if the actually known physical laws are not valid for these movements.

2) comets. Something with a 26,000 year orbit would be in the Oort and Kupier belts and we'd see comets raining down from that area
This is not a so strong objection, as there have been comets raining down in the past. We can be now in a relatively quiet part of the orbit. Also, the orbit's period can be bigger than 26000 years.
3) stellar evolution. Any star that is within a 26,000 year orbit is going to be seen.
Again, that is not a so strong objection. The sun can be in orbit with an invisible companion. Indeed, so called "dark matter" points in that direction.

This is just a totally nutty idea. There's a whole literature that places on the extra-solar system objects which are possible. Planet X and Nemesis. It's just one step above flat earth.
Let's say that for Polestar101 ideas to be valid, our actual understanding about how the physical universe works would have to be radically changed, or extended.

One problem is that most of the people on this thread are GR experts, and if you want to rule out the existence of a binary companion to the Sun, the strongest tests are not GR effects.
I know. I'm not interested in ruling out a binary companion (nor in the tests of GR in itself), but in precisely understanding the solar system movement in space, its causes, and its effects. Maybe GP-B results can be of any help in that regard. That's the reason I'm posting.

Mauro

So, can I ask you what is the presumed cause of these movements?
One of the things that Newton figured out is that if something moves in a straight line, there isn't a need to explain why it's moving in a straight line. You only need an explanation if something is curving or accelerating.

What's happening is that the stars in our region in space are moving in an orbit around the center of the milky way whose period is 220 million years. The sun has a random motion relative to its neighbors.

This probably should be carved off into another topic.

This a strong objection, and it's the main reason I disagree with Polestar101. If the solar system is moving in a curved path, that movement will produce parallax effects, not precession.
There are also tidal effects. If there was a gravitational object on one side of the solar system, you'd see stronger gravity on one end of the solar system than on other. There are limits to the size of "planet X" objects around the solar system, and a solar binary companion is exclude.

This is not a so strong objection, as there have been comets raining down in the past. We can be now in a relatively quiet part of the orbit. Also, the orbit's period can be bigger than 26000 years.
It's not so much the number, but the distribution of comets. If you have a gravitation object on one side of the solar system that would disrupt comets on that side more than the other, so we should see more comets coming in from one side of the solar system than the other.

Also the orbital period can be more than 26000 years which is the problem. Anything with an orbit of say 50,000 years is likely to interact with an object that has an orbit of 26,000 years.

The sun can be in orbit with an invisible companion. Indeed, so called "dark matter" points in that direction.
Even if the hidden companion was a black hole, you'd see it bend/block the stars behind it. The thing about a hidden companion is that you'd be able to quickly figure out the direction from observations, and even if it was a black hole, you'd see it bending the stars behind it.

Let's say that for Polestar101 ideas to be valid, our actual understanding about how the physical universe works would have to be radically changed, or extended.
No, that's not true. Science is a game in which people through up objections, people counter objections and so forth. The thing is that if you make any theory complicated enough you can explain anything, but if you can explain anything, you explain nothing.

I know. I'm not interested in ruling out a binary companion (nor in the tests of GR in itself), but in precisely understanding the solar system movement in space, its causes, and its effects. Maybe GP-B results can be of any help in that regard. That's the reason I'm posting.
One problem is that sometimes people with crackpot ideas get a false sense of how strong their ideas are by talking to scientists. Scientists tend to be super expert about one thing, but outside of the one thing, they just have average knowledge. So what happens is that if you have a nutty theory you can often get some scientist not to react at how nutty the idea really is, if the thing that kills the theory falls outside their area of expertise.

GP-B may not exclude the possibility of a solar companion, but it also doesn't tell us anything about the dinosaurs or how to make good tasting pizza. What really *kills* the idea of a solar companion are planetary motions.

One of the things that Newton figured out is that if something moves in a straight line, there isn't a need to explain why it's moving in a straight line. You only need an explanation if something is curving or accelerating.

What's happening is that the stars in our region in space are moving in an orbit around the center of the milky way whose period is 220 million years. The sun has a random motion relative to its neighbors.
So, this movement of the sun is not rectilinear and uniform. As something cannot be "random" and rectilinear and uniform at the same time.
Are the movements of the solar system towards the solar apex actually clearly understood and explained as caused by the gravity of the surrounding stelar environment? Can you point to papers or articles about this? Particularly: is the actual rate of change of this movement known?

Thanks,
Mauro

If other effects such as poholde and perturbing forces are eliminated then gyros 'point in a constant direction' in space. Garth
You can't simply eliminate polhode and other perturbing forces to save the experiment without first being able to exactly quantify these effects. And to try and measure them by eliminating anything that does not get to the GR goal is circular reasoning and bad science.

... the earth's wobble is such a well known and obvious effect that astronomers correct all of their measurements for it...
And this is the root of the problem. The earth’s wobble is indeed well known, measured and corrected for – so most scientists ‘assume’ that its theoretical cause (primarily lunisolar forces acting on the oblate earth) is a proven theory. Unfortunately, belief in a theory without questioning can have devastating results. In this case that unfounded belief wasted over \$800 million of taxpayer money on an ill conceived gravity experiment and earned GP-B the well publicized grade of 'F' from the NASA review board. The GP-B guys failed to consider unknown solar system motion relative to the guide star. Rather than question if conventional theories are correct they prefer to use polhode and other unquantifiable effects to fix their results.

It's something that they teach you to do in freshman astronomy classes
Good thing education doesn’t stop there. A deeper study of precession theory will show that Newton’s original equations didn’t work (and only temporarily came close after d”Alembert made assumptions about a non-rigid earth). Noticing the model’s inability to predict changes in the rate of precession over the last century scientists have repeatedly added and modified inputs resulting in the supposed final PN model in the year 2000 (2000A has almost 1400 terms and few realize it is forced to fit the observable). Alas, this problem has not escaped the IAU who in 2006 passed a resolution to say the precession nutation model “is not consistent with dynamical theory”. Read: it’s broken.

They don't matter for the purposes of this experiment, because as long as the sun is moving in a straight line, it's not accelerating and if it's not accelerating then they don't effect any experiments designed to measure acceleration.
Assuming the sun has no acceleration compounds the mistake and obfuscates the solution. Direct observations show the sun moves across the background stars at the rate of about 50” p/y. But convention assumes it doesn’t really do this because it assumes we are observing from a wobbling earth. And this is based on the assumption that lunisolar theory is correct so we deny the observation and constrain solar system motion to zero – and thereby conclude there can’t be any acceleration. Too many assumptions make for bad science. At the very least we should admit we don’t know where the sun is going and ask if there is any other way to explain its motion.

If the apparent motion of the stars moving across the sky at the rate of 30 degrees per month has been found to be due to an orbit (the earth’s orbit around the sun) it should not be inconceivable that the apparent motion of the stars moving across the sky at the rate of 30 degrees per 2000 years (a.k.a. the precession observable) might also be due to orbital dynamics (the orbit of the solar system around another mass). This is a simple concept but unfortunately when the cause of the later observable was hypothesized no one knew the solar system moved – and no one has bothered to rethink the problem (question Newton!?) since that time.

At BRI we’ve built a model to predict the changing rate of precession by applying Kepler’s laws to orbit parameters (24,000 year periodicity, apoapsis in 500AD) given by the Indian astronomer Sri Yukteswar in 1894, which he used to explain the precession observable. We then compared that model to the precession model given by the best astronomer of the same era, Simon Newcomb, and ran the two models from 1900 to 2000 then compared these to the actual precession rate reported in the Astronomical Almanac. The result is the Yukteswar orbit based model predicted changes in the rate of the precession observable 41 times more accurately than Newcomb’s lunisolar based model over the last 100 years. If predictability is the hallmark of science then the local dynamics model should be replaced with an angular velocity model as the later has proven a far more accurate way to predict changes in the so called precession rate over time.

Since you seem to be rational, I'll explain to you why his ideas (and I don't know of a nice way of saying this) are totally nutty.
Yes, it may be “nutty” to question conventional theory but it is even nuttier to blindly support a flawed theory. Let rational science and predictability, not convention, determine which theory is correct. It boggles the imagination that convention measures changes in the earth’s orientation to VLBI reference points far outside the moving frame of the solar system without accounting for any motion of that frame relative to those reference points. Does the earth not move with the solar system? Now that’s “nutty”!

Polestar

Also there are very strong limits on the existence of any extra solar star based on

1) celestial mechanics. Anything that could simulate axis precession would wreck havoc on solar system planetary motion
No exo-solar object “stimulates axis precession” because there is no classical precession to produce. The observable of the stars moving across the sky at the rate of 30 degrees per 2000 years is simply the observable of a solar system in motion, just as the observable of the stars crossing the sky at the rate of 30 degrees per month is caused by the orbital motion of the earth around the sun. The moon causes nutation and the tides – the precession observable has been misdiagnosed.

2) comets. Something with a 26,000 year orbit would be in the Oort and Kupier belts and we'd see comets raining down from that area
Scientists such as Whitmire and Matesse have suggested that long cycle comet activity is due to a companion but several scenarios suggest the object could be much much farther away (depending on the speed of the solar system). Remember we are not talking about a planet that revolves around the sun, we are talking about our sun (and entire solar system) revolving around a common center of mass with a very distant mass. As long as the distance between our furthest planet and the companion is at least 5x the distance of our furthest planet from our sun the perturbations on the planetary system would hardly be noticeable.

3) stellar evolution. Any star that is within a 26,000 year orbit is going to be seen.
It could well be that we do see it but don’t recognize it but it could also be a brown dwarf, red dwarf towards the galactic center, or even a blackhole. If astrophysicist Reg Cahill is correct the solar system is moving a lot faster than anyone believes – this opens up a lot of possibilities.

This is just a totally nutty idea.
Sitting on a mud ball hurtling through space – dark matter - communicating with electrons now – its all nutty, no question about it!

One problem is that most of the people on this thread are GR experts, and if you want to rule out the existence of a binary companion to the Sun, the strongest tests are not GR effects.
You are right. It is just that GP-B was a great experiment to detect motion of the solar system. Unfortunately, the team did not account for a moving reference frame relative to the guide star (far beyond their expectations) so they ended up with all sorts of "noise" they could not understand. They tried to save the experiment by calling it polhode - effects impossible to predict - but thankfully the NASA review board recognized the charade. By the way, I have no problem with the GR effects - but I am more interested in the "noise". : )

Polestar

sylas

... Imagine for a moment that there actually are unknown effects, whose causes are being mistaken in the GP-B experiment.
This is not really a useful direction. It's a truism that there may always be unexpected effects that we don't know and what we think we know is wrong.

The point is that the actual measurements have a level of uncertainty which limits the accuracy at which they can test the GR effects. To the extent that they can test any of the ideas we are considering, they confirm GR -- though not to the accuracy that was initially hoped.

There is no consistent detectable signal in the numbers found that might correspond to unknown effects. There may be unknown effects, of course -- this is true for any experiment. But the numbers say they unknowns -- such as alleged unusual or unexpected motions of the solar system -- are too small to be tested by this experiment.

The notion that they are just being ignored or assumed away is flatly false.

Cheers -- sylas

sylas

You can't simply eliminate polhode and other perturbing forces to save the experiment without first being able to exactly quantify these effects. And to try and measure them by eliminating anything that does not get to the GR goal is circular reasoning and bad science.
This doesn't make any sense at all. They DO quantify the podhole effect. It was quantified and understood and taken into account from the start. There is an additional effect which was stronger than anticipated; from a tiny residual change on the gyroscopes, which gives an additional effect on the motions. There is no doubt at all that this effect exists. Most of the work of the extended data analysis phase HAS been to quantify this effect -- and not by assumption. When quantified, it can be extracted to reveal any underlying signal.

This is an extra factor influencing the gyroscopes which was larger than anticipated, and has been at the root of the limited accuracy to which results could be given.

The description by Polestar101 is very misleading. It's not bad science at all -- it is precisely what science should do to test GR as well as they can without making assumptions. They quantify all influences and obtain the residual signal, which stands then as a test of the predictions from the frame-dragging effect. There is no assumption of GR involved in that process. Without the proper quantification of the electromagnetic forces, the accuracy of the test is very weak. With proper quantification, the test will improve, though it is unlikely to get to the level of 1% which had originally been hoped.

There's a nice summary of the issues in The Gravity Probe B Bailout, IEEE Spectrum, Oct 2008. This report is describing how the team was able to secure additional funding; and their own project page gives more on the existing funding. (Gravity Probe B -- current status -- updated November 12, 2009. The work is ongoing, and primarily this is focused upon quantifying the effects of the electromagnetic influences, so that they can be properly take into account -- without just making assumption -- and so improving the accuracy of the true independent test of GR.

First of all, do you accept Newtonian physics as a reasonable approximation for solar system dynamics. If you don't then we really have no basis for discussion since if you make up your own physics, you can get any answer you want.

No exo-solar object “stimulates axis precession” because there is no classical precession to produce.
I'm not talking about that. I'm talking about predictions about the location of the planets (i.e. were is Mars)? If you have a exo-solar object and you aren't totally rewriting the laws of gravity then this exo-solar object will influence the locations of the planets in a big way. Now if you are rewriting the laws of gravity than all bets are off.

Remember we are not talking about a planet that revolves around the sun, we are talking about our sun (and entire solar system) revolving around a common center of mass with a very distant mass. As long as the distance between our furthest planet and the companion is at least 5x the distance of our furthest planet from our sun the perturbations on the planetary system would hardly be noticeable.
Except that it's not. You have long period comets which are going to interact with this hypothetical star. There was some discussion a few years back about whether a companion star to the sun causing mass extinctions. The consensus now is that this isn't happening, but you are talking about a far more massive companion which would have much larger effects.

It could well be that we do see it but don’t recognize it but it could also be a brown dwarf, red dwarf towards the galactic center, or even a blackhole. If astrophysicist Reg Cahill is correct the solar system is moving a lot faster than anyone believes – this opens up a lot of possibilities.
So tell us what to look for and where to see it. It's OK to list the possibilities and then eliminate them.

You are right. It is just that GP-B was a great experiment to detect motion of the solar system.
Personally I don't think it is, since GP-B was trying to eliminate that as an effect.

Unfortunately, the team did not account for a moving reference frame relative to the guide star (far beyond their expectations) so they ended up with all sorts of "noise" they could not understand.
That's precisely what makes it a terrible experiment to look for what you are looking for. The first reaction of any physicist to any small effect is that it's noise, and the reason physicists have that reaction is that most of the time, it is. If you want to convince people that your theory is right, you have to come up with an experiment that has such a *HUGE* effect that you can't argue that it's noise. That's the job of a theorist. If the different is a few arcminutes, this is going to convince anyone. You have to come up with an experiment that is off by tens of degrees.

It occurs to me that the motion of Pluto is going to be a lot better experiment than anything that you can come up with in GP-B.

By the way, I have no problem with the GR effects - but I am more interested in the "noise". : )
I think GP-B is just the totally wrong experiment for you to focus your attention on, since they are trying to eliminate the effects you are looking for. The experiments are really sensitive and if there are any unexplained results they are small enough that people are going to conclude that it's just noise. You are wasting your time on GP-B, and you should be looking at something else.

Something that you should do (and I'm putting the work on you because you are the theorist) is to calculate the effect of your companion star on Pluto and compare that with the effects on Jupiter. If it's small, then try something else. You aren't going to convince anyone of anything by looking at small effects, you have to have a whopping big effect that no one can possibly explain by tweaking the variables.

That's what Polestar101 is saying, if I understood correctly. And I think that that's a possibility that clearly deserves a closer scrutiny.
Perhaps but not by GP-B.

Those are the known, small effects, predicted by GR. Imagine for a moment that there actually are unknown effects, whose causes are being mistaken in the GP-B experiment.
If the effects are small enough, then you'll never see them with GP-B. It's quite possible that there is some unknown effect that is being dismissed as noise by GP-B, and in fact I think it's quite likely that there is some unknown effect somewhere that is effecting GP-B. But the way that physicists do experiments, if it's not something that you are expecting then you aren't going to see it. The trouble is that it's hard to see something that you aren't looking for.

This happens all the time in science. People come up with a new idea and then they go back to old data and find that it was staring them at the face all the time. But to come up with the new idea usually involves a "smoking gun."

That's where theorists come in, and the job of a theorist is to come up with ideas for experiments which have effects that are far, far, far too large to be dismissed as noise. The reason don't think that Polestar101 is that he isn't accepting the fact that you are just never going to convince people that GP-B results are due to some companion star, and not looking for the smoking gun elsewhere. I'm trying to be helpful and I've come up with about three suggestions for what to look for.

So, this movement of the sun is not rectilinear and uniform. As something cannot be "random" and rectilinear and uniform at the same time.
Yes it can be.

Are the movements of the solar system towards the solar apex actually clearly understood and explained as caused by the gravity of the surrounding stelar environment?
It's not caused by the gravity of the surrounding stellar environment. The idea in both Newtonian and GR is that if something moves in a straight line, then there is nothing to explain. Gravity causes things to curve.

Probably not since in the framework of physics that most people use, there's nothing to explain.

Yes it can be.
I see. The official position on this is that the sun is moving on a straight line towards a random point.

It's not caused by the gravity of the surrounding stellar environment. The idea in both Newtonian and GR is that if something moves in a straight line, then there is nothing to explain. Gravity causes things to curve.
I know that, twofish-quant. The question would then be: how do scientists know that the Sun is moving in a straight line towards the solar apex?
Better yet: what amount of curvature would be acceptable given the actual knowledge of solar system motion? that is, assuming that a gently curved motion is assimilable to a straight line, for relatively short intervals of the curve, how gentle that curve must be?

Probably not since in the framework of physics that most people use, there's nothing to explain.
Well, it could be interesting to compare the results of Dunkin's 1880 paper on solar system motion, with a recent similar study of solar system motion. In more than a century a noticeable difference could show up, even if the statistical nature of the process will tend to obscure it.

Mauro

I see. The official position on this is that the sun is moving on a straight line towards a random point.
The official position is that all of the stars in this area are moving around the center of the galaxy. Now if you look at the sun's position relative to these stars, you'll see an extra "random" motion. There would be something weird if the sun's motions were different than the other stars in the region but they aren't.

The question would then be: how do scientists know that the Sun is moving in a straight line towards the solar apex?
I think the correct statement would be that the observations are consistent with the sun moving in a straight line toward the solar apex. The data is really noisy, so if there was some curvature I don't think you'd see it from stellar proper motion observations.

Better yet: what amount of curvature would be acceptable given the actual knowledge of solar system motion? that is, assuming that a gently curved motion is assimilable to a straight line, for relatively short intervals of the curve, how gentle that curve must be?
That's a great question. I don't think you can get this information from stellar evolution velocities measurements since you just have a snapshot of proper motions. One obvious constraint is planetary motions. Anything that causes the solar system to curve is going to create a "centrigual force" on the planets, which would change their orbits.

Something else that you can see are doppler shift changes to distant quasars. Changes in the CMB.

I'm not sure what the limits would be off hand, but they would be interesting to calculate. My gut feeling is that the limits would be on the order of meters per second.

Well, it could be interesting to compare the results of Dunkin's 1880 paper on solar system motion, with a recent similar study of solar system motion. In more than a century a noticeable difference could show up, even if the statistical nature of the process will tend to obscure it.
It would be, but comparing these sorts of datasets turns out to be hard because they are often noisy.

That's a great question. I don't think you can get this information from stellar evolution velocities measurements since you just have a snapshot of proper motions.
Thanks.

One obvious constraint is planetary motions. Anything that causes the solar system to curve is going to create a "centrigual force" on the planets, which would change their orbits.
Indeed.
The orbits of the planets seem to be changing. There's an unexplained lengthening of Sun-Earth distance, by example, which is measured with great precision using laser or radar ranging. I'll post the article or paper when I find it.
A lengthening of Sun-Earth distance over the semi major axis would be consistent with an acceleration of the Sun in the direction of the (northern) winter solstice, if I'm not mistaken.
It could be interesting to compare Sun-Earth distance changes over the semi-major axis vs. changes in distance at the equinoxes, i.e. to try to determine changes in the eccentricity of Earth's orbit.
Also, if the Sun is accelerating "laterally", the Sun-Earth distance at one of the equinoxes will tend to be smaller than at the other equinox, and the side of the smaller distance will be in the direction of the acceleration. And the amount will tell us something about the magnitude of the acceleration.
Comparative orbital dynamics! It seems that's all we need to know how and how much our direction in space is changing.

I'm not sure what the limits would be off hand, but they would be interesting to calculate. My gut feeling is that the limits would be on the order of meters per second.
Could be. Could be more. Could be changing.
My own estimate is that the limits would be on the order of some hundreds of meter per second maximum, because the estimations and measurements of velocity towards the solar apex(if they are correct, of course) are in the order of tens of kilometers per second. An amount two orders of magnitude smaller sounds like something that could be overlooked, specially if the data is noisy.

Regards,
Mauro

The orbits of the planets seem to be changing. There's an unexplained lengthening of Sun-Earth distance, by example, which is measured with great precision using laser or radar ranging. I'll post the article or paper when I find it.
Yes. The trouble is that there may be a thousand different things that could cause this, and you need some particular reason to believe that a curvature in the sun's motion is causing that as opposed to interaction with dark matter particles or mismeasurements in the mass of Jupiter. Something that I found interesting is that radiation pressure turns out to be able to change the motion of asteroids.

One problem I have with polestar is that he keeps picking small anomalies and not realizing that any of his ideas would result in much, much larger differences that those anomalies.

A lengthening of Sun-Earth distance over the semi major axis would be consistent with an acceleration of the Sun in the direction of the (northern) winter solstice, if I'm not mistaken.
And it's also consistent with a thousand other things. What you really need to get a smoking gun is to start with the assumption of acceleration, figure out all of the consequences, and then come up with some sort of obvious smoking gun. Just to give you one, if the you have an unexplained motion of the earth, and an unexplained motion of Mars and they are in the same direction that means something very different than if they aren't.

You can also work it the other way. Given what we know about the solar system, what is the maximum amount of acceleration that is possible? It's not zero.

My own estimate is that the limits would be on the order of some hundreds of meter per second maximum, because the estimations and measurements of velocity towards the solar apex(if they are correct, of course) are in the order of tens of kilometers per second. An amount two orders of magnitude smaller sounds like something that could be overlooked, specially if the data is noisy.
There is a dimensional problem here. Acceleration is in distance per second per second.

My suspicion is that the limits from the proper motion data are much worse than that since the data is so noisy. Something to point out is that one set of solar apex measures provide no obvious limits on the acceleration of the solar system, since you are just taking one snapshot. You need measurements over time, and I suspect even those are going to be extremely noisy. Also solar apex measures tell you nothing at all, if all the stars in the local region are getting accelerated in the same way as the sun.

Also this is all an interesting game, because you are always thinking of ways of getting tighter measurement.

There is a dimensional problem here. Acceleration is in distance per second per second.
You're right. I was thinking about changes in velocity during an interval of some years between observations or estimations, I suppose.

Some interesting related papers:
http://arxiv.org/abs/0907.2469" [Broken]
http://arxiv.org/abs/gr-qc/0604052" [Broken]
http://arxiv.org/abs/0904.1562" [Broken]
http://arxiv.org/abs/0907.4514" [Broken]

What would be interesting to do is to analyze the changes of the Sun-Earth distances at different points of the Earth orbit. That is, instead of working on trying to explain the general secular increase of the Astronomical Unit, to try to detect if there are specific sectors of the Earth orbit at which the distances are increasing / diminishing.
That could be a way to see if the changes are due to an acceleration of the Sun, or to other factors. Of course this is not so easy to calculate, because the effects of the different planets, particularly Jupiter, would have to be carefully taken into account, these planets are also moving, the sun-earth barycenter is changing, etc.
But this looks more promising than to try to compare historical statistical analysis of stelar proper motions.

Regards,
Mauro

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Curiously in looking at the references in one of the papers I found this

It uses millisecond pulsars to establish an acceleration limit of a/c~a few×10-19 s-1 which ends up being 3 x 10^-10 m/s/s

One thing that I find pretty amazing is that we seem to know length of the astronomical unit to with 3 *meters*, and the increase in the AU is 15 *cm* per year. This makes it really difficult to figure out whether the increase is higher in one part of the earth's orbit than another, since I don't you have the data to that resolution.

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Curiously in looking at the references in one of the papers I found this

It uses millisecond pulsars to establish an acceleration limit of a/c~a few×10-19 s-1 which ends up being 3 x 10^-10 m/s/s

One thing that I find pretty amazing is that we seem to know length of the astronomical unit to with 3 *meters*, and the increase in the AU is 15 *cm* per year. This makes it really difficult to figure out whether the increase is higher in one part of the earth's orbit than another, since I don't you have the data to that resolution.
I've found the original paper on the secular increase of the AU:
http://iau-comm4.jpl.nasa.gov/GAKVAB.pdf [Broken]

They are using comparations of radiometric distances to Mars stationed spacecraft.
That's why the precision is better than that of the AU itself.

I suppose this rules out my idea of studying distance asimetries on different sectors of Earth's orbit, unless a reliable method to measure distance to the Sun(distance measurement to a Sun's close orbiting spacecraft?) is established.

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I suppose this rules out my idea of studying distance asimetries on different sectors of Earth's orbit, unless a reliable method to measure distance to the Sun(distance measurement to a Sun's close orbiting spacecraft?) is established.
That's where the fun part of physics comes in. You often want to do something and you find out that for various reasons you can do it in the obvious ways, so you spend the next several months/years trying to figure out how to do it in a non-obvious way. You might want dig some more about exactly how the measurements are done.

Trying to figure out what correlates with the increase in the AU is interesting because it may turn out that when you look at the data, it doesn't correlate with the location of the earth at all but with the location of Mars. Something else that occurs to me (and I'm thinking out loud) it might be a good idea to compare observations that involve spacecraft and those that involve things that are planted on the ground.

One other thing that I'd find interesting is to try to see if there are any systematic differences between US, Russian, and European spacecraft, since it occurs to me that all of the anomalies seem to be associated with US spacecraft, and it would make me more confident that it's not equipment if you are able to repeat the results with Russian spacecraft using Russian equipment.