From: Anders Sandberg (asa@nada.kth.se)
Date: Fri Aug 16 2002 - 01:51:28 MDT
On Fri, Aug 16, 2002 at 07:14:41AM +0200, Amara Graps wrote:
> Anders Sandberg:
> >I honestly don't know how astronomers measure it for galaxies.
>
> The velocity is given by the redshift of the spectral lines, which
> is straightforward to measure for an individual galaxy. However,
> for measuring the velocity one must also consider the 'peculiar motions'
> of the galaxies moving with respect to each other ('peculiar velocity').
...
Thanks. But what about finding the tangential component of the peculiar
velocity?
I guess one can calculate it approximatively by assuming a randomly
directed peculiar velocity and that most galaxies move with roughly the
same velocity; then one can assume the tangential component is simply
large enough to produce a "normal" value of the total peculiar velocity.
But it still doesn't give any information on direction.
Another thing to do might be to look at the velocities of clusters, and
make assumptions about their mass and then solve for the orbits with
observed velocities as constraints. But that also seems highly
approximative.
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