Two expanding universe questions.....

Can anybody give me the answers to these two questions, please

1. Red shifts are used to decide how far away a distant object is.
It's difficult to imagine relative to what but these measurements
refer to how fast the object is moving away from us, the observer.
But, surely our galaxy is also affected by the expansion of the
universe so the red shift of a distant galaxy is due to it's own
relative motion PLUS our Milky Way motion. So, how do we know what
proportion of shift to use to calculate how far away the distant
object is?

2. As I understand it, the more distant an object is the faster the
expansion of the the universe that it is in. Thus, some galaxies must
be approaching the speed of light. When that velocity is close to 99%
of light speed then Einstein's relativity ideas come into play. Time
slows down and mass increases towards infinity. So, what becomes of
red shift measurements then?

Keep it simple please - I am but a simple man!

Pete L wrote:
Can anybody give me the answers to these two questions, please

1. Red shifts are used to decide how far away a distant object is.
It's difficult to imagine relative to what but these measurements
refer to how fast the object is moving away from us, the observer.

So far so good.

But, surely our galaxy is also affected by the expansion of the
universe so the red shift of a distant galaxy is due to it's own
relative motion PLUS our Milky Way motion. So, how do we know what
proportion of shift to use to calculate how far away the distant
object is?

Actually we can determine the local peculiar motion of our galaxy by
reference to the 4K microwave background surface of last scattering.
There is a detectable dipole moment that is due to Doppler shift from
our motion relative to the mean isotropic expansion.

The Andromeda galaxy is one rare example of a blue shifted galaxy - it
is headed towards us on a roughly collision course. Don't worry though
it will take a very long time to get here.

2. As I understand it, the more distant an object is the faster the
expansion of the the universe that it is in. Thus, some galaxies must
be approaching the speed of light. When that velocity is close to 99%
of light speed then Einstein's relativity ideas come into play. Time
slows down and mass increases towards infinity. So, what becomes of
red shift measurements then?

Keep it simple please - I am but a simple man!

The second is a much harder question to give a simple answer to.

On cosmological distance scales the Einstein GR field equations come
into play and the definition of the horizon needs careful consideration.
There is a zone of the (presumed infinite) universe that is already
moving away from us so fast due to expansion of the intervening space
that we will never see any photons from it.

In practice we can only see back to the point at which the universe
became transparent to electromagnetic radiation.

It is probably a bit heavier going than you asked for but the following
isn't a bad introduction and has most of the right pictures in:

http://www.astro.columbia.edu/~zolta...es/c3602.3.pdf

Regards,
Martin Brown