How do they measure the lateral (relative to us) movement of galaxies and what have you which are a gazillion light years away?
I understand that red shift can indicate how fast they are receding (or advancing) but how do they figure out lateral movement?
At those distances perceived movement must be really, really tiny.
My understanding is that they don’t, especially at the “gazillion light years” point. Even at distances as close as Andromeda, the lateral motion is not clear.
They don’t, really. I’m not an expert, but my understanding is that we only have an estimate of transverse velocity for a few extragalactic objects.
One technique that’s been used to do this is to look at so-called “satellite galaxies”, which are orbiting around a large galaxy that you want to figure out the velocity of. If there are a lot of these satellite galaxies moving around the major galaxy (think like a swarm of bees buzzing around a hive), and you make certain assumptions about the statistical distribution of the satellite velocities, you can actually extrapolate the transverse speed of the major galaxy from knowledge of the satellite velocities along the line of sight. This was done for the Andromeda Galaxy a few years back, and people have talked about trying to do it for more distant galaxies as well; however, I’m not sure if anyone has succeeded at this yet.
Finally, if things get moving really fast, then relativistic effects can kick in and you can end up with so-called “superluminal jets.” Nothing’s traveling faster than light in this phenomenon; it’s just an illusion caused by objects travelling near the speed of light almost directly towards us. But in these cases, the change in the positions of these jets is noticeable over a period of months or years.
There have been some attempts to measure proper motion of a few nearby galaxies. I don’t think they’ve done more than put upper bounds on them. That is, they haven’t actually measured the motions, but have been able to say that they don’t move more than some value.