"Grimble Gromble" wrote in message ...
"AA Institute" wrote in message
m...
So if the transverse velocity of Alpha Cen is 5.0 AUs/yr and the
radial velocity is -5.5 AUs/yr, does this mean that in 50,000 years
(272,000 AUs current distance / 5.5 AUs radial velocity) Alpha
Centauri is going to be very close to us?! Probably not, since due to
gravitational interaction with the Sun, Alpha Centauri might describe
a 'curved' trajectory as opposed to a linear one.
I've not checked your figures but assuming them to be correct: since the
transverse velocity is of the same order as the radial velocity, then by the
time the radial velocity 'would' have closed the distance between Alpha
Centauri and the Sun, the transverse velocity would have carried it just as
far at right angles and it will end up a similar distance away. The closest
approach would then be about 0.7 times the current distance.

Thanks Grim, silly me for not seeing the wood for the trees...
So the closest approach point for Alpha Centauri (around 3 LY) is
still yet to come? Hoooorrrraaayyy!!!

This could be the ideal interstellar *launch window* for the Aster-Com
starship. A future generation of Earth might face the challenging
choice of either taking this window of opportunity or declining the
offer in anticipation of another star passing by the Sun. But that's
gonna be a long, long time coming...

It would be so much easier to visualise the whole thing in a 3D diagram.
There are programs available for plotting just such things in 3D. I remember
mentioning Mathcad not too long ago! You can even allow a term for the
gravitational interaction between the stars and convince yourself that it
has little effect. I'd do it for you except I have more interesting projects
I would rather spend my time working on (no offence meant).

That's fair comment. Hey, what's the big deal with a 50,000 year
voyage inside some hollowed out gigantic boulder rolling across in the
deep, dark ocean of space toward some unknown destination
pre-programmed by your great great great grand parents? It sucks...

Also referring to memory, which, as I always remind everyone, is very dodgy,
I have a vague recollection that when the velocities of nearby stars are
compared, the stars essentially fall into two groups. Stars in our group
move pretty much in the same direction and speed as the Sun, while the other
group of stars travel in a direction and speed that is common to them and
different from ours. I believe there were other factors such as age and
composition that distinguished the two groups? I apologise if this is not
the case, however, like most things, I cannot remember my source.

No probs, really appreciate your thoughts.

One final question: interstellar navigation - how can I do it whilst
drifting in this great interstellar ocean where the shores reach out
to near eternity in every direction?

"In the extreme circumstance where no new bodies are found for meeting
projected resource requirements, the ship can turnaround and back
track towards previously charted bodies using emergency reserves. With
no magnetic fields, no bright planets, no "GPS" for relative
referencing, the minute positional shifts of nearby stars may be the
only method of interstellar navigation in the surrounding darkness of
3D space."

How can I precisely chart the *absolute* positions and ship-relative
velocities of icy comets encountered on a forward pass... then try to
re-intercept them on a reverse pass, having turned my ship around?

Abdul