# Solar System Moving Speed

• B
Hello Dear Ones.

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

thank you very much.

## Answers and Replies

berkeman
Mentor
Hello Dear Ones.

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

thank you very much.
Movement with respect to what?

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

or better - sun default movment speed.

phinds
Gold Member
2021 Award
...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?

russ_watters
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.

Nik_2213
phinds
Gold Member
2021 Award
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.

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

I think this measurement is absolutetly wrong, due lack of understading of simplicity of human mind. What is default speed ? Lets 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 doesnt 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 theres no doubt that WILL HAVE precisely measurment of units, of speed, energy. etc. This measurment is wrong , because is relative. not true. We dont 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
Gold Member
2021 Award
Technically speaking, that would be 'relative to the CMB rest frame', would it not?
Yes, you are correct.

phinds
Gold Member
2021 Award
I think this measurement is absolutetly wrong, due lack of understading of simplicity of human mind. What is default speed ? Lets 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 doesnt 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.

davenn and russ_watters
Please read my statments very carefuly. I SAID THAT we dont 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 gonna gave its own units. if you cannot feel space, its your own psychological problem

phinds
Gold Member
2021 Award
Please read my statments very carefuly. I SAID THAT we dont 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 gonna 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.

lomidrevo, davenn and Bystander
jim mcnamara
Mentor
@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
Mentor
Please read my statments very carefuly. I SAID THAT we dont 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".

davenn, Bystander and jbriggs444
Dale
Mentor
2021 Award
You can transform movement speed to termodynamical energy, and it gonna 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.

@shimun maybe you can start here, in order to get correct understanding of what is relative motion, and why there is nothing like "true" (or absolute) speed

Chronos
Gold Member
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
Gold Member
2021 Award
@shimun maybe you can start here, 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.

RandyD123, berkeman and davenn
Chronos
Gold Member
Listening does not alter the facts.

phinds
Gold Member
2021 Award
Listening does not alter the facts.
Yeah, but he had his own set of "facts".

davenn
Chronos
Gold Member
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.

I think this measurement is absolutetly wrong, due lack of understading of simplicity of human mind. What is default speed ? Lets 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 doesnt 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 theres no doubt that WILL HAVE precisely measurment of units, of speed, energy. etc. This measurment is wrong , because is relative. not true. We dont 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
Mentor
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.

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
Mentor
2021 Award
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.

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. Lets 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
Gold Member
2021 Award
...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?)

davenn and Bystander
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