62 million year extinction cycle

Allan Adler wrote:
When the Sun moves in its orbit, it bobs up and down in the equatorial plane
of the Milky Way. Why does it do that? If, for comparison, we look at the
orbit of the Earth in the solar system, is there any comparable bobbing
motion?

Paul's answers have been good, but I might add something here. In the
Solar System, we're used to thinking of just one planet at a time, but
really "the plane" should be the "invariable plane," i.e., the
weighted average of the planes of all the planets. Obviously that's
nearly but not exactly the same as the plane of Jupiter's orbit.

With respect to the invariable plane, all the planets "bob up and
down" with a period equal to their orbit period. This is very similar
to the Sun's "bobbing" in the Milky Way. The only difference is that
for the Sun in the MW, the "bobbing" period is not equal to the
orbital period because the MW mass distribution is different: disklike
rather than a single central mass.

To answer your later question about damping, I suppose dynamical
friction will have an effect, but only on long timescales. It's
really a statistical equilibrium problem, with random accelerations
and decelerations.

On Sep 12, 11:12 pm, (Paul Schlyter) wrote:
In article .com,

BradGuth wrote:
Even within the local realm of our vast Milky Way galaxy is simply of
what's for the most part too far away and moving further away at too
fast of velocity as to bother with,

Huh?

Our galaxy isn't internally expanding with the rest of the universe
but remains at approximately the same size. So the objects in our
Milky Way galaxy are approaching us just as often as they recede from
us. The approaching objects won't approach us all the way until they
collide with us, of course, but for now and for many years to come,
they are approaching us.

I actually agree, whereas instead of forever expanding it's going
rather nicely in and out on a 225 million year cycle, not to mention
whatever rogue stars and planets that haven't thus far been
documented. I only said what others in Usenet keep expecting us to
believe that most everything is supposedly moving away from us, which
of course and as you say it isn't.


And some of the galaxies on our local group are approaching us too - for
instance M31, the Andromeda galaxy, which eventually will collide with us
in the very far future. But a "collision" of two galaxies is more
like e.g. two swarms of bees passing through one another.

Perhaps our combined Oort clouds hosting icy debris the size or
possibly greater than our moon are actually a bit more populated than
whatever cosmic swarms of bees. All it takes is one such interaction
and all of cosmic hell is going to bust lose, especially testy if in
retrograde to one another.

Too bad there's not an available supercomputer or much less of any
interactive 3D orbital simulator, as otherwise all sorts of absolutely
nifty information could be tested out.
- Brad Guth -