In message , David Knisely
writes
Panius wrote:

This is the first time that i've heard an astronomer say this.
Most scientists still seem to believe that Andromeda will
collide with the Milky Way in about 5 billion years.
And i've been saying all along that the blue shift can only
show radial velocity, that Andromeda could be coming
in our general direction at an angle that would cause it to
miss us by a country megaparsec. That the chances of
it actually colliding with us could be slim to none.
Thanks, David, for this bit of validation. Do you know if
there are other astronomers out there who are warming
up to this view?

The only astronomers who are saying that M31 will (ie: with certainty)
collide with us are either those who are not very well versed in the
subject, or those who are trying for some headlines (I suspect the
latter). The radial velocity component of M31 (corrected for our
solar-system's rotation about the Milky-Way's galactic core) has been
known for at least several decades, so when I heard about someone
trumpeting about a "collision", I said to myself, "Its probably
grant-renewal time again", as you see these sort of news releases put
forward by groups hoping to get enough publicity to justify the
continuation of funding.

Isn't the point that the transverse velocity is unknown? How big would
it have to be before we can be certain that M31 will miss us (bearing in
mind that M31's radial velocity is well below "our" galaxy's escape
speed?) And is there any chance of measuring the transverse velocity,
for instance by measuring the position of the centre of M31 relative to
distant objects such as quasars?
--
Rabbit arithmetic - 1 plus 1 equals 10
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