Trojan

[Strange]

If we claim that the Sun goes up and down with reference to the galactic disc due to the gravity, than it must be vertical to the disc (exactly at 90º).

Why?

[Hornblower]

One thing that tickles me is that Dave Lee keeps on invoking Kepler in his remarks about gravity, when Kepler never got as far as a theory of gravity, or a quantitative force theory of any sort concerning orbital motion. Kepler's three well known "laws" are simple kinematic formulas he derived empirically by analyzing observable motions. They are in good but not perfect agreement in the special case of the planets orbiting the Sun. Newton showed how they follow from the gravitational theory he developed, for the special case of a large central mass and vanishingly small planetary masses. He and his successors showed that the same theory accounts for the departures from pure Keplerian motion when the planetary masses are not vanishingly small. These departures include precession of the plane of a reference ellipse, with an extreme case being the proportionately rapid up and down oscillation of the Sun's galactic orbital motion through the galactic equatorial plane.

[czeslaw]

The oscillations will not last for ever. The energy is exchanged by the vacuum which is not theoretically empty.
The collision of a pair of neutron stars, marked by ripples through the fabric of space-time and a flash brighter than a billion suns, has been witnessed for the first time in the most intensely observed astronomical event to date.

The extraordinary sequence, in which the two ultra-dense stars spiralled inwards, violently collided and, in all likelihood, immediately collapsed into a black hole, was first picked up by the US-based Laser Interferometer Gravitational-Wave Observatory (Ligo).
https://www.theguardian.com/science/...nse-event-ligo

Greetings
Ceslaw

[cjameshuff]

The oscillations will not last for ever. The energy is exchanged by the vacuum which is not theoretically empty.
The collision of a pair of neutron stars, marked by ripples through the fabric of space-time and a flash brighter than a billion suns, has been witnessed for the first time in the most intensely observed astronomical event to date.

The extraordinary sequence, in which the two ultra-dense stars spiralled inwards, violently collided and, in all likelihood, immediately collapsed into a black hole, was first picked up by the US-based Laser Interferometer Gravitational-Wave Observatory (Ligo).
https://www.theguardian.com/science/...nse-event-ligo

Greetings
Ceslaw

The oscillations will last far longer than the sun itself. We are not discussing gravitational radiation or other dissipative effects, the OP doesn't even understand the most basic parts of Newtonian mechanics and is arguing for cycles and epicycles as a model of stellar motions.

[czeslaw]

The oscillations will last far longer than the sun itself. We are not discussing gravitational radiation or other dissipative effects, the OP doesn't even understand the most basic parts of Newtonian mechanics and is arguing for cycles and epicycles as a model of stellar motions.

You are right, because the distances between the sun and stars are relatively large. Nevertheless the spiral disc was created from a round cloud not an everlasting disc.

[grant hutchison]

Thanks for this answer.
It is a proof that you agree that there are contradictions between the diagram and the theory. (Otherwise, you won't offer this answer).
So, our scientists set this diagram by monitoring the Sun movement and with massive calculations.
In order to explain that orbital outcome, another group had offered a theory.
I have proved that there are contradictions between the two.
If you think that there is an error in the calculation - than it is expected to fix it.
Otherwise, you have to fix the theory.

Yes, there is a mismatch between the diagram and theory. This is because the diagram is wrong, and doesn't represent the theory. There is the added complication that you are also misunderstanding the diagram.
You'd be well served by ignoring the diagram and paying attention to what people are explaining to you.

Grant Hutchison

[cjameshuff]

Yes, there is a mismatch between the diagram and theory. This is because the diagram is wrong, and doesn't represent the theory.

To add to this: it is not our responsibility to fix every poorly drawn diagram on the internet.

[grant hutchison]

There is another issue:
Gravity works vertically.

Please see the following message:

So as the sun moves around the galaxy, it also goes up, stops moving upwards, and then comes down again.
And as the ball in Jens's example moves from thrower to catcher, it also goes up, stops moving upwards, and then comes down again.

Direct question: Do you agree with that?

Grant Hutchison

So, if the Sun stops at the top pick, it must come vertically to the galactic center.
This isn't the case with our Sun.
So, there is one more contradiction.

And you still haven't responded to the question of mine that you quote. If nothing else, it would be polite to do so.

Gravity pulls the sun "vertically" down to the galactic plane, not to the galactic centre. Because gravity in a disc is not a central force.
I'll say that again.
Gravity in a disc is not a central force.

That is really important. You've been told it a number of times, by a number of people, in a number of ways.
That property of Newtonian gravity is fundamental to the calculations that show the sun passing repeatedly up and down through the galactic plane as it moves around the galaxy.

And that's the other important thing, which you've been told multiple times:
The "bobbing" trajectory of the sun has been derived entirely from the mathematics of Newtonian gravity.
There can be no incompatibility between the two, because the one has been used to derive the other.

The issue here is not that there is something unexplained about the sun's trajectory, but that you have mistaken preconceptions that are preventing you from understanding the explanation.

Grant Hutchison

[Dave Lee]

And you still haven't responded to the question of mine that you quote. If nothing else, it would be polite to do so.
Grant Hutchison

What was the question please?

Gravity pulls the sun "vertically" down to the galactic plane, not to the galactic centre. Because gravity in a disc is not a central force.
I'll say that again.
Gravity in a disc is not a central force.

Grant Hutchison

Thanks for your message.
It was a typo Error.
My intention was galactic disc and not Galactic Center.

And that's the other important thing, which you've been told multiple times:
The "bobbing" trajectory of the sun has been derived entirely from the mathematics of Newtonian gravity.
There can be no incompatibility between the two, because the one has been used to derive the other.

The issue here is not that there is something unexplained about the sun's trajectory, but that you have mistaken preconceptions that are preventing you from understanding the explanation.

Grant Hutchison

Ok
Let's agree that there is no problem with the Sun.
Let's agree that its Bobbing movement is perfectly according to our Theory.

However, what about the nearby stars?

Please look at the following Diagram:

https://www.quora.com/If-planets-and...l-system-so-on

We see clearly that each star is moving randomly to different direction.

You can get better visibility on that in the following:
http://www.ifa.hawaii.edu/~barnes/ast110/MilkyWay.pdf

Pg 15.

If "Gravity pulls the sun "vertically" down to the galactic plane":

I would expect that if the entire nearby stars are bobbing around the galactic plane, than they should move with some sort of synergetic (Up / Down)
This is not the case - based on the attached diagram.

It is quite clear that some of them aren't located at the Galactic Disc and it could be that they are even moving parallel to the Disc (above or below the disc).

How can you explain that random motion directions?
Why the galactic plane has no impact (almost zero) on the directions of those stars?
Don't you think that it is a contradiction to our Theory?

Or as usual - there is a problem with the diagram.

[Dave Lee]

Now,

Just consider an option that each star orbits around its unique center of mass.
Don't you think that there is a perfect match to what we see in this diagram (If the diagram is correct)

[czeslaw]

Our Sun oscillates not only in one Orion Arm. It goes slowly apart from the galactic centre far away into the galactic halo where reside the very old stars. It is not a simple rotation and bobbing around the center of the galaxy. The clouds and gas falls down into the galactic plane where the stars are born and than rotate slowly toward the farther arms till to the halo.
http://curious.astro.cornell.edu/phy...y-intermediate

The matter on cosmic scale has really move with some sort of synergeti (Up/Down) and create cosmic pancakes.
https://en.wikipedia.org/wiki/Zeldovich_pancake

[grant hutchison]

What was the question please?

The one you quoted, and which I've been asking you in alternate posts for some considerable time now.

So as the sun moves around the galaxy, it also goes up, stops moving upwards, and then comes down again.
And as the ball in Jens's example moves from thrower to catcher, it also goes up, stops moving upwards, and then comes down again.

Direct question: Do you agree with that?

Say "Yes" or "No".

Ok
Let's agree that there is no problem with the Sun.
Let's agree that its Bobbing movement is perfectly according to our Theory.

However, what about the nearby stars?

Please look at the following Diagram:

https://www.quora.com/If-planets-and...l-system-so-on

We see clearly that each star is moving randomly to different direction.

You can get better visibility on that in the following:
http://www.ifa.hawaii.edu/~barnes/ast110/MilkyWay.pdf

Pg 15.

If "Gravity pulls the sun "vertically" down to the galactic plane":

I would expect that if the entire nearby stars are bobbing around the galactic plane, than they should move with some sort of synergetic (Up / Down)
This is not the case - based on the attached diagram.

You really need to stop trying to reason from diagrams you don't understand.
That diagram shows the residual movement of stars relative to the Local Standard of Rest. The Local Standard of Rest is a reference frame moving around the galaxy at orbital velocity - about 250 km/s. The residual movements you see in that diagram are of the order of a few kilometres per second.
So what you are seeing is the effect of all the stars in our local neighbourhood bobbing up and down without synchrony and with their own characteristic frequencies and slightly differing trajectories, but all sweeping around the galaxy at a couple of hundred kilometres per second.

Or as usual - there is a problem with the diagram.

As usual, there is a problem with your understanding of the diagram.

You can find out more about the Local Standard of Rest, galactic kinematics and how different star populations inhabit different disc thickness because of their characteristic velocity distributions here (1.5 MB pdf).

Grant Hutchison

[PetersCreek]

What was the question please?

The one you quoted, and which I've been asking you in alternate posts for some considerable time now.

Dave Lee, you need to do a lot of catching up on unanswered questions. Back in post #128, Swift warned you:

Dave Lee

This thread is rapidly going nowhere.

You need to start directly answering all the questions that have been put to you, not just the ones you think are interesting. You need to address all of them systematically.

And you need to start offering a very clear explanation of what EXACTLY you are claiming and you need to present some evidence for those claims. Evidence does not consist of repeated, incorrect assertions by you, nor links to imprecise drawings or vague articles by others.

You need to start doing this immediately, or this thread will be closed.

Please get to work. Do not move on to any other points until you've directly answered all pending questions.

[Hornblower]

What was the question please?



Thanks for your message.
It was a typo Error.
My intention was galactic disc and not Galactic Center.


Ok
Let's agree that there is no problem with the Sun.
Let's agree that its Bobbing movement is perfectly according to our Theory.

However, what about the nearby stars?

Please look at the following Diagram:

https://www.quora.com/If-planets-and...l-system-so-on

We see clearly that each star is moving randomly to different direction.

You can get better visibility on that in the following:
http://www.ifa.hawaii.edu/~barnes/ast110/MilkyWay.pdf

Pg 15.

If "Gravity pulls the sun "vertically" down to the galactic plane":

I would expect that if the entire nearby stars are bobbing around the galactic plane, than they should move with some sort of synergetic (Up / Down)
This is not the case - based on the attached diagram.

It is quite clear that some of them aren't located at the Galactic Disc and it could be that they are even moving parallel to the Disc (above or below the disc).

How can you explain that random motion directions?
Why the galactic plane has no impact (almost zero) on the directions of those stars?
Don't you think that it is a contradiction to our Theory?

Or as usual - there is a problem with the diagram.

No, there is a problem with your interpretation of the diagram, as has been the case with so much of what you have posted in this thread. If we could watch these stars for enough millions of years, we could see them bobbing in the same manner as the Sun, but not necessarily in phase with it. We could be on an upward excursion through the disk while a nearby star is on its downward half of its corresponding cycle, and 30 million years later we could be going down while the other star is going up. It would be like two pendulums side by side, swinging in opposite directions. The stars with horizontal motion relative to the sun can be explained by being in orbits with about the same period but different amounts of eccentricity and with their lines of apsides in different orientations. Over the course of a full orbit they would appear to oscillate around their mean positions.

[Dave Lee]

You do also realise the diagram you refer to is not even remotely to scale? The diameter of the solar system is measured in light hours - the thickness of the disc is roughly 1000 light years. Our solar system is comfortably embedded inside the disc, even at the peaks & troughs of its oscillations.

Wow,
Sorry that I have missed you great explanation.

So, "Our solar system is comfortably embedded inside the disc, even at the peaks & troughs of its oscillations"
Hence, the Sun is wobbling inside the galactic disc.
In all the diagrams which I have seens, it is clear that the Sun is wobbling in and out from the galactic disc plane As follow:
http://www.slate.com/blogs/bad_astro..._is_wrong.html
"A far more correct (though exaggerrated vertically for clarity) depiction of the Sun's motion around the Milky Way galaxy has it bobbing up and down every 64 million years due to the gravity of the galactic disk."

However, Now I understand that the Sun never ever goes out the Disc.
So how could it be?

It is stated that at the disc the gravity power on the object is virtually zero. In order to get the wobbling momentum you have to jump above or below the disc.

In the article it is stated clearly:
"If you are slightly above the disk you feel an overall pull down, toward the disk. Imagine the disk is just a huge slab of matter, and the Sun is above it. The gravity of the disk would make the Sun plunge down into it."

Yes, that is feasible If you are slightly above the disk .
But now it is clear that our sun is always inside the disc. It never gets out.
Therefore, there is no option for: "If you are slightly above the disk".
In this case, our Sun should not get any sort of wobbling momentum!!!

I have used a trampoline example.
So, if you jump on a trampoline Net while keeping the energy conservation than you can keep it forever.
Please see the excellent explanation by Jens:

"

I surmise that you are starting from the idea of a bouncing ball, which eventually stops bouncing. But you probably have heard about the conservation of energy, so in a sense the ball should keep bouncing forever. The reason it stops bouncing is that the energy is transferred to the surface (for example, you can hear a sound, which comes from vibrations caused by the impact), and to the air because of friction. In a perfect vacuum with a perfectly elastic collision, the ball would keep bouncing forever. The stars are essentially in a vacuum, so they will keep oscillating nearly forever.

However, if you are located inside the Net (with a Thickness of about 1000 m, while your height is only 2m. for example), how can you actually even start to jump?
You are locked inside the Net.
No Up, No down.

Now try to explain how can you jump or wobble forever while you are locked by the net/disc?

[VQkr]

In all the diagrams which I have seens, it is clear that the Sun is wobbling in and out from the galactic disc plane As follow:
http://www.slate.com/blogs/bad_astro..._is_wrong.html
"A far more correct (though exaggerrated vertically for clarity) depiction of the Sun's motion around the Milky Way galaxy has it bobbing up and down every 64 million years due to the gravity of the galactic disk."

Did you miss the "greatly exaggerated" part? You really need to quite taking schematic diagrams literally. They are learning tools to explain a specific point; they break if you apply them elsewhere.

Now try to explain how can you jump or wobble forever while you are locked by the net/disc?

The Milky Way is not a trampoline net; it is not dense.

[VQkr]

Sure

However, the elliptic orbital cycle of each planet is in two dimension.
"The inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit. It is the angle between the orbital plane and the plane of reference, normally stated in degrees. "

Therefore, as stated, this example does not represent a case that the orbital object is zig zag (Up Down or In out) several times during one orbital cycle.

Approximately. If you ignore the gravity of the rest of the solar system and treat each planet's orbit as a 2-body system with the sun. That's an adequate simplification for many purposes, but it doesn't translate at all to stellar trajectories in a galaxy.

[Strange]

Yes, that is feasible If you are slightly above the disk .
But now it is clear that our sun is always inside the disc. It never gets out.

"Above the disk" and "inside the disk" are not contradictory statements. The gravitational force from the disk will only be zero at the plane of the disk, if you are above that (but still inside the disk) there will be a restoring force pulling you down.

I have used a trampoline example.

Well don't. Use some actual physics instead of making stuff up.

[AGN Fuel]

As VQkr pointed out, you have ignored the warning that the vertical motion in the diagram was "greatly exaggerated". You also ignored a point I made earlier in the same paragraph you quoted that the disc in the vicinity of our sun was 1000 light years thick (a conservative figure btw).

To try and help the penny finally drop, imagine this greatly simplified scenario:
Assume an equal distribution of stars, gas & dust, etc above and below the mid plane of the disc. This means that at the exact mid plane of the galactic disc, there is a equal density above and below any object 'sitting' there. However, an object located halfway to the upper 'edge' of the disc will have 3/4 of the local mass 'below' it and only 1/4 of the local disc mass above it. That object there will feel a net gravitational force taking it back toward the mid plane even though it is still 250 light years within the disc.

That object will descend back down toward the mid plane under the effect of that net gravitational force, but (remember your old pal Newton? Do you recall his first law?), it will continue moving down through that plane. As it travels below the plane, the amount of mass 'above' the object becomes greater than 'below' it, so the object starts to experience a net gravitational force pulling it (now back up) toward the midline again. The object will reach 250 light years from the bottom 'edge' of the disc before ascending back through the disc, past the mid plane of the disc toward its starting point.

There being practically nothing to stop this motion, it will continue oscillating up and down in this manner effectively forever. Now, imagine that object is also moving orthogonally to this up and down motion. The combination of motions results in a lovely wave motion within the disc. Which is the motion of the sun that we have been trying to explain to you for 6 pages.

[Dave Lee]

As VQkr pointed out, you have ignored the warning that the vertical motion in the diagram was "greatly exaggerated". You also ignored a point I made earlier in the same paragraph you quoted that the disc in the vicinity of our sun was 1000 light years thick (a conservative figure btw).

To try and help the penny finally drop, imagine this greatly simplified scenario:
Assume an equal distribution of stars, gas & dust, etc above and below the mid plane of the disc. This means that at the exact mid plane of the galactic disc, there is a equal density above and below any object 'sitting' there. However, an object located halfway to the upper 'edge' of the disc will have 3/4 of the local mass 'below' it and only 1/4 of the local disc mass above it. That object there will feel a net gravitational force taking it back toward the mid plane even though it is still 250 light years within the disc.

That object will descend back down toward the mid plane under the effect of that net gravitational force, but (remember your old pal Newton? Do you recall his first law?), it will continue moving down through that plane. As it travels below the plane, the amount of mass 'above' the object becomes greater than 'below' it, so the object starts to experience a net gravitational force pulling it (now back up) toward the midline again. The object will reach 250 light years from the bottom 'edge' of the disc before ascending back through the disc, past the mid plane of the disc toward its starting point.

There being practically nothing to stop this motion, it will continue oscillating up and down in this manner effectively forever. Now, imagine that object is also moving orthogonally to this up and down motion. The combination of motions results in a lovely wave motion within the disc. Which is the motion of the sun that we have been trying to explain to you for 6 pages.

Thanks for the explanation.
However, in the article it is stated clearly:
"If you are slightly above the disk you feel an overall pull down, toward the disk. Imagine the disk is just a huge slab of matter, and the Sun is above it. The gravity of the disk would make the Sun plunge down into it."
The Sun is never ever above the disc at any given time. This is clear to all of us.
I was sure that this key discovery will help all of us to understand that there is a severe contradiction with that Theory.
The whole wobbling activity was based on a simple idea that the Sun must cross the disc.
So, even if it cross "slightly above the disc" that could be still O.K.

Now, when we all know that the Sun does not cross the disc at any given time ("even at the peaks & troughs of its oscillations"), we have to find new idea to protect that Theory.

And the New idea is:
"Assume an equal distribution of stars, gas & dust, etc above and below the mid plane of the disc."

And if not? how do you know that?
Why do you assume that there is equal distribution of stars, gas & dust, etc above and below the mid plane of the disc?
Any proof for that assumption?

As we have no proof, let's try to find it.
Let's look at the nearby stars:

List of nearest stars and brown dwarfs
https://en.wikipedia.org/wiki/List_o...d_brown_dwarfs

"This list contains all known stars and brown dwarfs at a distance of up to 5 parsecs (16.3 light-years) from the Solar System. In addition to the Solar System, there are another 56 stellar systems currently known lying within this distance. These systems contain a total of 60 hydrogen-fusing stars (of which 50 are red dwarfs), 13 brown dwarfs, and 4 white dwarfs. "

Based on this list, please try to advice:
1. Why do you think that there is equal distribution of stars?
2. How could it be that those 60 stars (with random mass, random locations, random velocities, random speed directions...) should help the Sun to wobble?
Please don't forget that we expect that they will fulfill the same wobbling activity. So, how can they Push and pull the Sun while they have to push and pull themselves?

[tusenfem]

Based on this list, please try to advice:
1. Why do you think that there is equal distribution of stars?
2. How could it be that those 60 stars (with random mass, random locations, random velocities, random speed directions...) should help the Sun to wobble?
Please don't forget that we expect that they will fulfill the same wobbling activity. So, how can they Push and pull the Sun while they have to push and pull themselves?

NO, enough is enough.
You are NOT here to ask questions, you are here to answer the questions that are put to you.
You hvae been told several times now to make work on answering stuff, and it is time you start.
To help you on your way, an infraction for you, maybe that will be an incentive.

[Swift]

And the thread is closed.

Dave Lee - upon your return, if you wish to reopen this thread, you will Report this post and explain in detail how prepared you are to answer questions.