Expert: Tom Whiting - 11/29/2009

Question
I shall try to clarify my original question:  The moon orbits the earth.  The Earth Orbits the the Sun.  The Sun orbits the Galaxy.  The Galaxy orbits ???,  ??? orbits ???.  My knowledge does not go beyond The Sun orbits the Galaxy.  Does any more Orbiting take place.  If so, where is the stopping place?

Answer
The Milky Way appears to have a random motion inside the Local Group. That's capital L and G.
(Our Local Group is a collection of some 30 or so galaxies within about 5 million lightyears - including us, Andromeda (M-31), the Pinwheel (M-33), several other spirals, and about 25 dwarf galaxies).
Our galaxies' specific motion within the Local Group is on a collision course with Andromeda
(M-31) or near collision, which will occur in 4-6 billion years. The two galaxies are closing
on each other at about 200 miles per second, but are still separated by nearly 2.9 million
lightyears.

Now the Local Group is orbiting (and is a member of) the Virgo Supercluster (of Galaxies) out there in Virgo about 65 million lightyears distant. This cluster includes M's 84, 86, 87, and thousands of other galaxies.
The Virgo Supercluster is participating in the general spacial expansion according to the
Hubble constant of about 71 Km/sec per megaparsec, thus moving away from all the other
superclusters of galaxies.  For instance, the Coma Group, the Hercules Group, the Perseus
Group, etc.  It's not that there is little rockets attached to the galaxy
clusters, it's the space itself expanding (and accelerating it's expansion as time goes by)
and the galaxy clusters are just going along for the ride, similar to an un-manned canoe
going down a mountain stream faster and faster.  Or it's like a loaf of raison bread in an
oven....each galaxy supercluster is one of the raisons, so the most distant raison moves
away the fastest.  Doesn't matter which raison you pick as your "home" galaxy, as they all
move apart proportionally to their distance from each other as the 'bread' rises.
And the oven is getting hotter and hotter so the raison bread is rising (expanding) faster
and faster as time goes by. (Big question of today is, is the acceleration....accelerating too?)
Plus, the entire known Universe may be slowly rotating too, we just don't know yet.
That's as far as we can go now.

Yes, the moon orbits the Earth, but the Earth also orbits the moon. Technically, they orbit
a common baricenter, but that line is buried well within the Earth itself.
Just thought I'd clarify that too.
Hope all this helps...the bottom line being that there is no such thing as absolute rest in
the Universe; everything is moving relative to everything else. There is no "stopping" in space,
(Irrespective of Capt. Kirk as he brings the Enterprise to a "full stop"...
...relative to...what?  That solar system off the Port side?  The star Rigel up ahead?
The star Altair right behind them?) ?????????
... because you're always in motion relative to something...and they to you.
Clear Skies,
Tom Whiting
Erie, PA