# Our solar system speed

Saint
Can someone tell me, how fast is our solar system moving in space relative to a static coordinate system in space?

Mentor
100,000,000,000,000,000,000,000 mph with regard to the Russ Universal Coordinate System (RUCS)

Um, if you didn't get the sarcasm, based on Einstein's relativity, there is no static coordinate system in space.

Saint
Originally posted by russ_watters
100,000,000,000,000,000,000,000 mph with regard to the Russ Universal Coordinate System (RUCS)

Um, if you didn't get the sarcasm, based on Einstein's relativity, there is no static coordinate system in space.

however, it is moving right ?
movement is defined by speed and acceleration,
if no static coordinate, what about Relative coordinate?

meteor
The velocity of the Sun in its movement around the center of the Milky Way is 250 km/s. The Sun do a complete rotation in 225 million of years, so since the formation of the galaxy must have done 52 rotations more or less
You may think that the galaxy rotates like a rigid body, but it's not the case. The stars, in its rotation, follow kepler laws, so the stars that are more near to the center of the galaxy, move more rapid than the stars more far away
Like system of coordinates you can choose the same galaxy at a given moment

Mentor
Originally posted by Saint
however, it is moving right ?
movement is defined by speed and acceleration,
if no static coordinate, what about Relative coordinate?
Yes, you can find a speed for the solar system based with respect to any object you want. But most would be arbitrary and/or meaningless. meteor's example of using the center of the galaxy is about the best we can do. There is nothing further away that makes sense to use as a center point.

In Einstein’s relativity there is no claim that a static coordinate system does not exist, since every coordinate system can be defined to be static with respect to some other. The point is, whether it exists a coordinate system which can be considered as ‘static’ with respecto the observable universe. From the point of view of Einsteins relativity principle, such a coordinate system would be as arbitrary as any other, but from the point of view of the question placed here it would be surely the best one. This coordinate system turns out to be the CMB (Cosmic Microwave Backgound). If one takes enogh amount of matter, it’s center of mass will in rest relative to the CMB. This has already been proven in studies after Lauer and Postman in 1994. The velocity of the solar system can be derived from the dipolar anysotropy of the CMB and is about 600 km/s in the direction of the geat attactor, a colossal matter structure far behind the milky way.

Regards.

Staff Emeritus
Gold Member
And strangely enough, most of the developing theories of quantum gravity (string theory and loop quantum gravity) involve a preferred rest frame -- most people automatically assume the universe's preferred standard of rest is the CMB frame.

Before relativity, there was a notion of a universal standard of rest. After relativity, there was none. After quantum gravity, there may yet be one again....

- Warren

Gold Member
Dearly Missed
This question came up in the "Astronomy" thread fairly recently. The CMB anisotropy was measured by COBE and the result of 4 years of measurement was reported in Astrophysical Journal in 1996.

http://arxiv.org/PS_cache/astro-ph/pdf/9601/9601151.pdf [Broken]

the solar system is moving in the direction of the constellation Leo at a speed of 370 km/s, with respect to the CMB.

Here's a quote from the article, with their confidence interval
for the speed:

369.0 +/- 2.5 km/s

galactic coords (264.31 degrees, +48.05 degrees)

celestial coords (11 h 11' 57", -7.22 degrees)

temperature delta 3.358 millikelvin

Here is what chroot posted in the Astronomy thread, which sums up the situation without all the extra decimal places

QUOTE]Originally posted by chroot
Like I said, 370-390 km/s in the direction of Leo.

- Warren
[/QUOTE]

Our galaxy is moving in a different direction, and the Local Group of galaxies is moving in a slightly different direction from that.

Chroot gave a reference to an arXiv paper that says where the Local Group of galaxies is heading and how fast. It is in the constellation Crater and IIRC around 600 km/s. The arXiv paper said 627 km/s. Here is the reference:

http://www.arxiv.org/abs/astro-ph/0210165

There is only about 20 degrees difference in the sky between the solar system's direction and that of the Local Group, tho velocities rather different

It is the solar system's motion that we see most clearly in the Microwave Background. The spot we are heading for is blueshifted (hotter by about 3 millikelvin) and the spot we are going away from is redshifted (colder by 3 millikelvin).

Cosmologists tend to use a stationary frame-----stationary with respect to what cosmologists call the Hubble flow, same as not moving with respect to the expansion of the universe-------thermonuclear described this!----also same as not moving w/rt the Microwave Background.

So it is a slightly differenet attitude and and perspective that cosmologists have, they have an idea of rest frame and simultaneity and observer-at-rest, whereas in Special Relativity its different. There is no absolute at rest, no fixed idea of simultaneity---everybodys motion is relative and so on.

this is why the motion of the solar system (specifically the solar system) is so important and measuring the hotspot/coldspot "anisotropy" of the CMB is so important-----and one reason COBE is famous as an orbital observatory. Because knowing the solar systems motion w/rt the universal rest frame gives astronomers their HANDLE on the universal rest from----so they can plot everythng else they want to referred to the rest frame.

They rarely give standing ovations at AAS conferences. COBE got one when its team gave the first report (George Smoot et al)
That is when you started seeing blotchy blue and red ovals around in magazines. Snapshot of universe beginning etc.
One of these powerful images of the universe---like the planet earth shot-----that tells something (in this case where we are going in terms of the universe's absolute notion of rest, and a whole lot else besides but that anyway for starters)

Thermonuclear would be right if instead of the solar system what he means is the Virgo Supercluster----itis indeed moving towards the Great Attractor in the Hydra-Cenataurus direction (a still different part of the sky) and it is the biggest concentration of mass in the neighborhood of our local group of galaxies.

But it can be confusing to have too many directions discussed.
So what I remember is our solar system going towards Leo and that is where the CMB hotspot actually is in the sky.

Originally posted by thermonuclear
In Einstein’s relativity there is no claim that a static coordinate system does not exist, since every coordinate system can be defined to be static with respect to some other. The point is, whether it exists a coordinate system which can be considered as ‘static’ with respecto the observable universe. From the point of view of Einsteins relativity principle, such a coordinate system would be as arbitrary as any other, but from the point of view of the question placed here it would be surely the best one. This coordinate system turns out to be the CMB (Cosmic Microwave Backgound). If one takes enogh amount of matter, it’s center of mass will in rest relative to the CMB. This has already been proven in studies after Lauer and Postman in 1994. The velocity of the solar system can be derived from the dipolar anysotropy of the CMB and is about 600 km/s in the direction of the geat attactor, a colossal matter structure far behind the milky way.

Regards.

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May be I misunderstood both posts after mine, but I think I've to disagree, if you belive that the possibility of defining the CMB as a reference frame in rest to the observable universe, means that the relativity principle has to be revised.

In my oppinion this fact means only that the postulate of homogeneity of the matter/matter flow distribution in the universe is correct and does not (necessarily) imply any claim about the relativity principle, i.e. that the laws of physics should be the same in all frames of reference.

Further on, as far as I know, some of the quantum gravity approaches just postulate a deformation of the mass shell equation. This also does not (necessarily) mean that the relativity principle has to be revised, as G. Amelino-Camelia has already shown in his Double Special Relativity three years ago.

Regards.

Gold Member
Dearly Missed
Originally posted by thermonuclear
May be I misunderstood both posts after mine, but I think I've to disagree, if you belive that the possibility of defining the CMB as a reference frame in rest to the observable universe, means that the relativity principle has to be revised.

The CMB rest frame is the standard one to use in Cosmology.

You are referring to an idea in ***special***relativity.
There is a notion of an inertial frame in SR and laws of physics
are the same in all inertial frames. In SR there is no one distinguished rest frame and no universal idea of simultaneity.

Cosmology and ***general***relativity do not contradict SR (they apply to different situations and model different aspects of reality from SR). But people are always running into the APPARENT logical conflict between SR and the other two.

Cosmology has a distinguished rest frame which you always see cosmologists using---indeed the Robertson Walker metric is based on it. Cant help this, just the way they do it. Seems to work fine though. By talking more one can reconcile this with the earlier SR view.

Eric Linder has some nice notes called Cosmology Overview. Short, completely mainstream, and to the point. Might like em.
Ned Wright's tutorial, as always, is great. Both will help clarify this