B Solar System Moving 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?

 

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.

 

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.

 

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

 

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

 

Yes, you are correct.

 

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.

 

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.

 

@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.