Peculiar motion and acceleration of local standard of rest

Does the "Local Standard of Rest" orbit the centre of Milky Way on a
perfect circular orbit?

It should be verifiable - what is the radial velocity of the centre of
Milky Way?

Why should it not be? Well, there are the spiral arms. Are those
purely a gas formation? And even then, they should cause some movement
of star field. Therefore, the general star field ought to move
collectively in and out with the passage of spiral arms. Is the local
standard of rest observed to be undergoing such?

Dear Crown-Horned Snorkack:

On Sep 24, 9:11 am, Crown-Horned Snorkack
wrote:
Does the "Local Standard of Rest" orbit the centre
of Milky Way on a perfect circular orbit?

No.

It should be verifiable - what is the radial velocity
of the centre of Milky Way?

Why should it not be? Well, there are the spiral
arms. Are those purely a gas formation?

No, it is oscillations of groups of stars... just like waves. Gas may
or may not be involved in local "brightening".

And even then, they should cause some movement
of star field. Therefore, the general star field ought
to move collectively in and out with the passage of
spiral arms. Is the local standard of rest observed
to be undergoing such?

Yes, I believe we are above the median of the galactic disk, and
heading for crossing. Something we do every few million years.

David A. Smith

Crown-Horned Snorkack wrote:

Does the "Local Standard of Rest" orbit the centre of Milky Way on a
perfect circular orbit?

It should be verifiable - what is the radial velocity of the centre of
Milky Way?

It's usually taken as being circular enough for most purposes. It's
probably pretty close, but not exact.

Why should it not be? Well, there are the spiral arms. Are those
purely a gas formation? And even then, they should cause some movement
of star field. Therefore, the general star field ought to move
collectively in and out with the passage of spiral arms. Is the local
standard of rest observed to be undergoing such?

The spiral arms are caused by density waves that push stellar creation;
they're not physical objects (they couldn't be, because with
differential rotation they'd wind tighter and tighter and eventually
disapppear).

But yes, the Solar System moves in and out of spiral arms. We're
currently on a small spur of an arm (variously called Orion Arm, Orion
Spur, Local Arm), in between two larger spiral arms.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
Think twice before you speak to a friend in need.
-- Ambrose Bierce

On 25 sept, 10:01, Erik Max Francis wrote:
Crown-Horned Snorkack wrote:
Does the "Local Standard of Rest" orbit the centre of Milky Way on a
perfect circular orbit?

It should be verifiable - what is the radial velocity of the centre of
Milky Way?

It's usually taken as being circular enough for most purposes. It's
probably pretty close, but not exact.

Exactly. Does anyone know how far it deviates from circular? And in
which direction?

Why should it not be? Well, there are the spiral arms. Are those
purely a gas formation? And even then, they should cause some movement
of star field. Therefore, the general star field ought to move
collectively in and out with the passage of spiral arms. Is the local
standard of rest observed to be undergoing such?

The spiral arms are caused by density waves that push stellar creation;
they're not physical objects (they couldn't be, because with
differential rotation they'd wind tighter and tighter and eventually
disapppear).

If they are density waves then they are physical objects and possess a
gravity field.

But yes, the Solar System moves in and out of spiral arms. We're
currently on a small spur of an arm (variously called Orion Arm, Orion
Spur, Local Arm), in between two larger spiral arms.

Do we know the direction and speed of movement of Orion Arm?