B Thank you for understanding. Have a great day!

[shimun]

Hello Dear Ones.

1. How Scientists exactly calculated movement speed of solar system ?

thank you very much.

 

[berkeman]

Hello Dear Ones.

1. How Scientists exactly calculated movement speed of solar system ?

thank you very much.

Movement with respect to what?

 

[berkeman]

Also, have you read through this long related thread?

https://www.physicsforums.com/threa...sun-and-solar-system-in-the-milky-way.888643/

 

[shimun]

-Speed of Sun Around Milky Way 230km/s. - This One.

 

[shimun]

or better - sun default movment speed.

 

[phinds]

...default movment speed.

That does not appear to be a meaningful phrase. What do you have in mind? Do you understand that all motion is relative and that it is meaningless to say speed unless you say relative to what?

 

[CygnusX-1]

The speed of the Sun around the Milky Way is around 250 kilometers per second. See Bland-Hawthorn and Gerhard (2016). Most of this speed is due to the Milky Way's rotation velocity, which is around 238 kilometers per second in the solar neighborhood. However, the Sun's orbit is slightly elliptical and we are currently closer to the Galactic center than usual, so we are moving about 12 kilometers per second faster than the Galaxy's orbital speed. 238 + 12 = 250.

This speed is much less than the speed of the Local Group of galaxies through the universe. As discussed in the October 2018 issue of Sky & Telescope, that is about 630 kilometers per second. It arises from galaxy clusters that try to pull us their way as well as voids that try to push us away.

 

[Bandersnatch]

-Speed of Sun Around Milky Way 230km/s. - This One.

There are various methods, but usually it involves measuring radial velocity to some object or objects using a spectrometer. The Doppler shift of some reference spectral lines in the light of the observed object reveals its relative velocity along the line of sight.
The problem with using single-object radial velocities as a proxy for solar orbital velocity is that one has to find something that can be reasonably treated as at rest w/r to the centre of the Milky Way, which is difficult.
But one can instead measure velocities of a large ensemble of objects, and use clever statistics to disentangle orbital velocity from the data.
Below is one such clever paper, published recently:
DETECTION OF A DEARTH OF STARS WITH ZERO ANGULAR MOMENTUM IN THE SOLAR NEIGHBORHOOD, Hunt et al.
It uses both radial and tangential velocities (provided by spectrometry and parallaxes respectively) to look at the distribution of velocities of neighbouring stars. There's a dip in the expected distribution, which can be attributed to scattering of low angular velocity stars by gravitational interactions in the galactic nucleus. The interactions fling some of these stars away to the galactic halo, removing them from the distribution. This dip provides a reference frame for being at rest w/r to the galactic centre. The relative velocity of such stars w/r to the Sun is then the negative of orbital velocity.

One can follow the references discussed in the introduction section of the linked publication to find other papers, using different methods, which all converge around the same value for orbital velocity.

 

[phinds]

This speed is much less than the speed of the Local Group of galaxies through the universe.

RELATIVE TO THE CMB ! You really should state that since this thread is at a beginner level.

 

[Chronos]

Technically speaking, that would be 'relative to the CMB rest frame', would it not?

 

[shimun]

I think this measurement is absolutetly wrong, due lack of understading of simplicity of human mind. What is default speed ? Let's be simple in thoughts. sun is moving, no doubt. we can reduce this movement to the simple movement of object trough infinite space, imagine as dot moving trough black space. so if its moving it has its own energy, and ITS OWN SPEED , it doesn't matter how is relative with other cosmical objects are, it moves, it has is OWN speed. We looking for is true speed, not relative speed. So if you imagine this movement as dot in black infinite space and you will put other immovable object in front of movement trajectory, after collosion sun as dot to for example to wall, will transform kinetical energy to another kind of energy and there`s no doubt that WILL HAVE precisely measurment of units, of speed, energy. etc. This measurment is wrong , because is relative. not true. We don't measure what speed of object is relation to other object, because it will give wrong result, we looking for speed of object in subject, as sun in space, its own.

 

[phinds]

Technically speaking, that would be 'relative to the CMB rest frame', would it not?

Yes, you are correct.

 

[phinds]

I think this measurement is absolutetly wrong, due lack of understading of simplicity of human mind. What is default speed ? Let's be simple in thoughts. sun is moving, no doubt. we can reduce this movement to the simple movement of object trough infinite space, imagine as dot moving trough black space. so if its moving it has its own energy, and ITS OWN SPEED , it doesn't matter how is relative with other cosmical objects are, it moves, it has is OWN speed. We looking for is true speed, not relative speed.

This is complete and total nonsense. You really need to come to grips with the fact that all motion is relative. There IS no absolute speed as you think there is. You are arguing against science that was established LONG ago.

 

[shimun]

Please read my statements very carefuly. I SAID THAT we don't look for relative speed, we looking for its true speed. relative speed is just comparison of two movement speed of objects. WE measure object speed in SPACE. You can transform movement speed to termodynamical energy, and it going to gave its own units. if you cannot feel space, its your own psychological problem

 

[phinds]

Please read my statements very carefuly. I SAID THAT we don't look for relative speed, we looking for its true speed. relative speed is just comparison of two movement speed of objects. WE measure object speed in SPACE. You can transform movement speed to termodynamical energy, and it going to gave its own units. if you cannot feel space, its your own psychological problem

Again. Total nonsense. There IS NO "true speed". ALL speed is relative. Space is just geometry. There is nothing to "feel"

@shimun a standard law is this: when you find yourself in a hole, stop digging. I suggest you do some reading in the basics of physics/cosmology before you go any further.

This forum is here to help people overcome misconceptions such as exactly the one that you have but we don't have infinite patience and if you persist in your incorrect statement that there is an absolute speed, this thread will likely be shut down since it is pointless to argue with such statements. You would be much better off accepting that you are wrong and trying to figure out why.

 

[jim mcnamara]

@shimun - We are here to help. But it requires that you get the concept that you are misinformed, and your original question was flat wrong by accepted standards.
You need to understand the concept of a frame of reference:
https://en.wikipedia.org/wiki/Frame_of_reference

Several very nice graphics in that article.

 

[russ_watters]

Please read my statements very carefuly. I SAID THAT we don't look for relative speed, we looking for its true speed.

Since you won't listen to @phinds, I'll repeat: there is no such thing as "true speed".

 

[Dale]

You can transform movement speed to termodynamical energy, and it going to gave its own units.

As others said, there is no absolute speed. If you transform movement speed to heat then all you have done is measure the original speed relative to the frame where the object came to rest. The math works out the same regardless of which frame that is. So it does not provide any additional information.

 

[lomidrevo]

@shimun maybe you can start http://physics.ucr.edu/~wudka/Physics7/Notes_www/node47.html, in order to get correct understanding of what is relative motion, and why there is nothing like "true" (or absolute) speed

 

[Chronos]

All speed is coordinate dependent, like every fraction has a denominator. Without a coordinate system [reference frame] the very concept of speed lacks any meaning.

 

[phinds]

@shimun maybe you can start http://physics.ucr.edu/~wudka/Physics7/Notes_www/node47.html, in order to get correct understanding of what is relative motion, and why there is nothing like "true" (or absolute) speed

All speed is coordinate dependent, like every fraction has a denominator. Without a coordinate system [reference frame] the very concept of speed lacks any meaning.

Presumably due to a couple of posts that have been deleted (and who knows what else) the OP has left the building. He DEFINITELY was not interested in listening to us.

 

[Chronos]

Listening does not alter the facts.

 

[phinds]

Listening does not alter the facts.

Yeah, but he had his own set of "facts".

 

[Chronos]

This is a powerful position from which to pose arguments. The silliness does not become apparent until the argument collapses under its own weight. This is a historically popular debugging tool. If, when confronted with additional facts, results do not agree with predictions, a proposition has only two choices: 1] be revised to avoid paradox; or 2] fail. When in doubt, apply Olber's rule.

 

[stefan r]

I think Galileo did a good job with an illustration. I supposes a jar full of flies. They fly in various direction at fly flight speed. Galileo can have one jar on the pier and measure the velocity of the flies. Another jar is on board one of the ships in the harbor. An observer on the ship sees the flies flying at standard fly flight speed. But the ship is passing Galileo so some of the flies have much higher velocity and some much lower.

 

[RandyD123]

I think this measurement is absolutetly wrong, due lack of understading of simplicity of human mind. What is default speed ? Let's be simple in thoughts. sun is moving, no doubt. we can reduce this movement to the simple movement of object trough infinite space, imagine as dot moving trough black space. so if its moving it has its own energy, and ITS OWN SPEED , it doesn't matter how is relative with other cosmical objects are, it moves, it has is OWN speed. We looking for is true speed, not relative speed. So if you imagine this movement as dot in black infinite space and you will put other immovable object in front of movement trajectory, after collosion sun as dot to for example to wall, will transform kinetical energy to another kind of energy and there`s no doubt that WILL HAVE precisely measurment of units, of speed, energy. etc. This measurment is wrong , because is relative. not true. We don't measure what speed of object is relation to other object, because it will give wrong result, we looking for speed of object in subject, as sun in space, its own.

That entire statement is just FALSE. You can mix and match your thoughts any way you like, but they would ALL still be wrong. Listen to what others are saying here because they are trying to help you get an understanding of real facts, not alternative facts!

 

[berkeman]

That entire statement is just FALSE. You can mix and match your thoughts any way you like, but they would ALL still be wrong. Listen to what others are saying here because they are trying to help you get an understanding of real facts, not alternative facts!

The OP is not here any more...

Presumably due to a couple of posts that have been deleted (and who knows what else) the OP has left the building.

 

[jeremyfiennes]

On Eddington's expanding balloon-surface model, a preferred 'at-rest' for speeds would be 'stationary on the balloon surface' – in practical terms: 'with respect to the CMB'. But since such a universe has no preferred direction, there are no absolute velocities (speed + direction).
Now imagine a rotating disk with two balls at opposite points on its circumference, attached to each other by a spring. When the disk rotates the spring is stretched, When it is stationary it is not. So there is an everyday rotational 'at-rest'. And since rotation is 'coordinated translation' – every point on the disk moves instantaneously translationally in a direction perpendicular to its radius – how come there can be everyday absolute rotation, but no absolute translation?

 

[Dale]

a preferred 'at-rest' for speeds would be 'stationary on the balloon surface' – in practical terms: 'with respect to the CMB'.

That is preferred in the sense “here is some matter relative to which we personally prefer to draw our coordinates. It is not preferred in the physical sense that the laws of physics are unique in that frame.

And since rotation is 'coordinated translation' – every point on the disk moves instantaneously translationally in a direction perpendicular to its radius – how come there can be everyday absolute rotation, but no absolute translation?

Because not all sequences of translations are inertial.

 

[alantheastronomer]

shimun said in post #4

Speed of Sun around Milky Way 230km/s

shimun said in post #11 in response to Bandersnatch's post #8

I think this measurement is absolutely wrong...We are looking for it's true speed, not relative speed.
This measurement is wrong, because it is relative. We don't measure what speed of an object is in relation to another object, because it will give a wrong result...

I think I understand what shimun is trying to say - and I agree! A measurement of a velocity relative to other objects in motion will not result in an objective observation. Let's think for a moment about a merry-go-round. The horses in the middle will see the horses closer to the center move at a slower relative velocity while seeing the horses near the edge move faster. Any conclusion the middle horse makes based on these relative velocities is bound to not be the horses "true" velocity. For that you need an impartial observer on the ground, one who does not take part in the carousel's motion. The disk of the galaxy is like the carousel. shimun is right to be suspicious about trying to draw any conclusions about our velocity around the center of the galaxy based on stars that are participating in the disk's motion. Fortunately for us, we have something like the impartial observer on the ground. What shimun didn't get from Bandersnatch's post, is that there are stars in the galactic halo, a spherical region outside of the disk, that don't participate in the disk's rotation. Some of these stars are even distributed in the disk near our location. These stars can be identified because they have very little heavy elements in their composition and this shows up in their spectra, and so these stars can be excluded from being disk stars. We can then use these stars to establish our velocity about the galaxy's center.

 

[phinds]

...I think I understand what shimun is trying to say - and I agree!

Well, you shouldn't. Velocity IS relative. You are digging yourself into the same hole that ended up with him not being here any longer (see that line through his name?)

 

[stefan r]

Lets think for a moment about a merry-go-round. ... you need an impartial observer on the ground,

The world spins around the merry-go-round. The observer off the merry-go round is not an impartial.

 

[Bandersnatch]

@phinds I don't think Alan is digging himself into anywhere. One does need to identify a 'stationary' frame of reference to measure our orbital velocity against. It's an interesting problem.
By assuming that's what the question was about, he's just giving the OP the benefit of the doubt - as one should be inclined to. Although, judging by OP's later responses, it appears undeservedly so.

What shimun didn't get from Bandersnatch's post, is that there are stars in the galactic halo, a spherical region outside of the disk, that don't participate in the disk's rotation. Some of these stars are even distributed in the disk near our location. These stars can be identified because they have very little heavy elements in their composition and this shows up in their spectra, and so these stars can be excluded from being disk stars. We can then use these stars to establish our velocity about the galaxy's center.

Looks like that's a different method from the one in my link. Do you know of any specific papers using it? I wonder how accurately one can identify halo stars from spectroscopy only.

 

[phinds]

@phinds I don't think Alan is digging himself into anywhere.

His direct quote was in support of that poster's nonsense.

 

[bahamagreen]

If we imagine in some inertial reference frame there are two objects in relative motion,
are there inertial reference frames in which the two objects are not in relative motion?

 

[phinds]

If we imagine in some inertial reference frame there are two objects in relative motion,
are there inertial reference frames in which the two objects are not in relative motion?

Any frame in which one of the objects is not in motion is going to be a direct translation to one of the original frames so by definition the other object will have to be in motion in that frame, so no.

 

[bahamagreen]

That's what I thought... so with regard to the two objects can you say, "There is motion" without qualifying it as some kind of relative motion?
What would you call this intrinsic motion that can't be removed by switching frames and does not depend on absolute rest with which to be relative?

 

[phinds]

That's what I thought... so with regard to the two objects can you say, "There is motion" without qualifying it as some kind of relative motion?
What would you call this intrinsic motion that can't be removed by switching frames and does not depend on absolute rest with which to be relative?

There IS NO "intrinsic motion". All motion is relative and it is always incorrect to state velocity without stating what that velocity is relative to. You call any motion just "motion" but you have to say what it is relative to.

If you have object A and in its rest frame there is an object B that is moving at 100mph, there are an infinite number of other inertial frames in which object B has a corresponding infinite number of velocities.

 

[bahamagreen]

There IS NO "intrinsic motion". All motion is relative and it is always incorrect to state velocity without stating what that velocity is relative to. You call any motion just "motion" but you have to say what it is relative to.

If you have object A and in its rest frame there is an object B that is moving at 100mph, there are an infinite number of other inertial frames in which object B has a corresponding infinite number of velocities.

May we go one step at a time? How do you logically disagree with this:

If there are no IFRs in which the two objects aren't in motion,
then one can conclude, "There is motion"
without stipulating either an absolute or relative reference.

 

[phinds]

May we go one step at a time? How do you logically disagree with this:

If there are no IFRs in which the two objects aren't in motion,
then one can conclude, "There is motion"
without stipulating either an absolute or relative reference.

Well, you can never legitimately say that there is motion of ONE BODY without saying what it is in motion relative to. Yes, you can say that two objects are in motion relative to each other but I don't see that that gets you anything. If you want to talk about one of the bodies you STILL have to say what it is in motion relative to, you cannot simple say "it is in motion".

 

[Dale]

May we go one step at a time? How do you logically disagree with this:

If there are no IFRs in which the two objects aren't in motion,
then one can conclude, "There is motion"
without stipulating either an absolute or relative reference.

You can probably say that they are moving relative to each other. That can be said without specifying any specific inertial frame because it is true in all inertial frames. However, technically it may not be true since you could construct non inertial frames where they are both at rest (assuming they don’t collide). But failing to qualify it is unlikely to cause confusion.

 

[lomidrevo]

I wonder how accurately one can identify halo stars from spectroscopy only.

I've just recently read about the kinematics of the Milky Way, and what I understood is that info about metallicity can be combined with observed peculiar motion of the stars (relative to the local standard of rest LSR). In particular, stars with large value of velocity component toward the galactic pole (perpendicular to the disk) are mainly to be identified as old, metal-poor stars, like red dwarfs. These stars are considered as being memebers of the stellar halo. So as I understand it, spectroscopy alone is not sufficient.

 

[alantheastronomer]

info about metallicity can be combined with observed peculiar motion of the stars

Yes, the two methods are used in concert, reinforcing each other's findings. However, low metallicity alone is the very definition of population II halo stars. The high observed relative velocities are an artifact of their being halo stars, not the prime indicator. Pop. I stars might have a peculiar velocity mimicking a halo star; it's metallicity can then be used to rule it out. The textbook "Galactic Astronomy" by Mihalas and Binney describes these methods. The relative motion that the OP hadn't realized he was referring to, was with respect to the center of the galaxy.

 

[Tom.G]

Just to confound matters.

If you are on an object in free space and you suddenly experience an increase (or decrease) in apparent gravity due to acceleration of the object, would it be appropriate to conclude that the motion of the object has changed?

 

[lomidrevo]

However, low metallicity alone is the very definition of population II halo stars. The high observed relative velocities are an artifact of their being halo stars, not the prime indicator. Pop. I stars might have a peculiar velocity mimicking a halo star; it's metallicity can then be used to rule it out.

But, vice versa, isn't the case that metal-poor, population II stars can be also part of the galactic thick disk or bulge? If yes, you would need the peculiar velocity measurements anyway to filter them out when identifying the actual halo stars. I must fully agree with your first sentence :)

Yes, the two methods are used in concert, reinforcing each other's findings.

...
Maybe dividing the stars only into two categories (population I and II) is somehow artificial in this context, in reality there is no strict border and the metallicity is changing continually. The ranges of star's metallicity might be somehow overlapping in various galactic structures.

 

[lomidrevo]

Just to confound matters.

If you are on an object in free space and you suddenly experience an increase (or decrease) in apparent gravity due to acceleration of the object, would it be appropriate to conclude that the motion of the object has changed?

I am not sure I understand the situation you described. What do you mean by apparent gravity? You and the object would experience the same change of the gravitational acceleration. If you were at rest relative to the object before the change, you would be at rest to the object after the change of the gravitational field.

 

[phinds]

Just to confound matters.

If you are on an object in free space and you suddenly experience an increase (or decrease) in apparent gravity due to acceleration of the object, would it be appropriate to conclude that the motion of the object has changed?

Yes, because for an increase in acceleration to be due to an actual increase in gravity, that would require magic to suddenly increases the mass of the object you are on so if you feel acceleration you know you are changing velocity.

 

[alantheastronomer]

But, vice versa, isn't the case that metal-poor, population II stars can be also part of the galactic thick disk or bulge? If yes, you would need the peculiar velocity measurements anyway to filter them out when identifying the actual halo stars. I must fully agree with your first sentence :)...
Maybe dividing the stars only into two categories (population I and II) is somehow artificial in this context, in reality there is no strict border and the metallicity is changing continually. The ranges of star's metallicity might be somehow overlapping in various galactic structures.

Yes, you're absolutely right; you need kinematics to separate the bulge stars from the halo. I'm glad you brought up the thick disk; it's an area of controversy that persists to this day! The thick disk is an observed density enhancement out to roughly 1000kpc (while the thin disk extends only 400kpc). There are two major theories for the origin of the thick disk; 1) As the early galaxy settled down from a spherical distribution, a second generation of star formation occurred in a thick disk just before finally becoming the thin spiral disk.2) Stars from the thin disk are being kinematically "slingshot" by Giant Molecular Clouds (GMC's) out of the plane of the Milky Way(like a satellite being given a gravity assist by a giant planet) "puffing up" into a thick disk.
Recently, abundance measurements seem to favor the former. So you're also right in that the thick disk should kind of be looked at as a sort of pop. 1+1/2...

The pop. II stars, including halo, bulge, and globular clusters, were all formed in one fell swoop, roughly all at the same time and so are considered one population. Their metallicities don't change. The thin disk on the other hand is comprised of a significant amount of gas, and so star formation is continually ongoing. As heavier elements are continuously being produced and mixed into the gas, the metallicity of the disk stars is continuously changing; as you mention.

 

[rootone]

Please read my statements very carefuly. I SAID THAT we don't look for relative speed, we looking for its true speed. relative speed is just comparison of two movement speed of objects. WE measure object speed in SPACE. You can transform movement speed to termodynamical energy, and it going to gave its own units. if you cannot feel space, its your own psychological problem

I think where you are going wrong is in having an idea that there some absolute frame of reference.
There isn't.

 

[phinds]

I think where you are going wrong is in having an idea that there some absolute frame of reference.
There isn't.

The OP CLEARLY didn't want to hear that (have you followed this thread? We said that to him over and over). He has left the building. See post #21