Proper motion in the universe

[losfomot]

When looking at the universe on a large scale, we see galaxies moving away from us proportional to distance. This is due to expansion. What I'm wondering is... disregarding expansion, is there a lot of motion in the universe? Or is everything pretty static.

[insane_alien]

well, andromeda is hurtling towards us at a few hundered kilometers per second and we have a few smaller galaxies orbiting us and several sub-galaxies getting absorbed into the milkyway. theres a lot of motion but if you zoom out far enough it all kind of looks static.

[Martin]

most common way to measure motion is with respect to the CMB

 

the motion of the solar system wrt CMB is about 380 km/second

 

the motion of Milkyway galaxy wrt CMB is about 500 km/second

 

It is about the same for other members of our local group of galaxies

Andromeda is moving in about the same direction as we are but a little faster (what I remember is about 50 km/second faster)

so that it is catching up with us and will eventually merge with us.

 

But that kind of merger speed is small (on the order of 50 if I remember right) compared with the overall LOCAL GROUP SPEED of some 500.

 

You might be interested to know the DIRECTION that our little group of galaxies is moving (at 500 km/second)

 

It is in the general direction of Hydra-Centaurus constellations, which BTW is where socall great attractor is believed located and some other galaxy clusters like Virgo Cluster are also moving roughly in that direction. It is in the Southern Hemisphere and the direction is marked by the constellations of Hydra and Centaurus.

 

But our local group velocity is not EXACTLY aimed at hydra-centaurus. It is more exactly in the direction marked by a smaller constellation called Crater ("drinking cup" in Greek) that looks like a rounded cup outlined by stars. It is a small constellation in the general hydracentaurus neighborhood in the southern sky. I can see it from the latitude SF.

 

all these speeds and direction are relative to the CMB, which is the standard way of presenting that kind of info,

 

relative to CMB also is expressed by astronomers a different way, they sometimes talk about motion "with respect to the Hubble flow" (which means with respect to the expansion of distances, and comes down to the same thing as measuring wrt the Cosm. Micro. Background)