Galactic Coriolis Effect

Main Question or Discussion Point

I was wondering if anyone could debunk or prove the theory of a Galactic Coriolis effect. That is, that stars and planets rotate one way in one hemisphere of the galaxy, and rotate in the opposite direction in the other hemisphere, similiar to how the swirling of water is affected in the Northern and Southern hemispheres on Earth.

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Janus
Staff Emeritus
Gold Member
First off, the the idea that water swirls down a drain in different directions in different hemispheres is a myth. The Coriolis effect just isn't strong enough over regions that small to overcome other random factors such as any latent angular momentum in the water to start with or even irregularites in the geometry of the drain. The Coriolis effect only comes into play over large regions like hurricanes.

That being said, planets and stars (or even entire planetary systems) are too small(compared to the galaxy) for any galactic Coriolis effect to play any significant role.

First off, the the idea that water swirls down a drain in different directions in different hemispheres is a myth. The Coriolis effect just isn't strong enough over regions that small to overcome other random factors such as any latent angular momentum in the water to start with or even irregularites in the geometry of the drain. The Coriolis effect only comes into play over large regions like hurricanes.
I thought if all things were equal (ie same drain, same angular momentum, etc.) then water would swirl in different dirrections based on the Coriolis effect, no?

Janus
Staff Emeritus
Gold Member
I thought if all things were equal (ie same drain, same angular momentum, etc.) then water would swirl in different dirrections based on the Coriolis effect, no?
No. The shape of the drain and the original momentum of the water would have a much greater effect and cause the water to swirl in the same direction.

The only way you could get different direction spin under exactly equal conditions is if the water starts with near zero angular momentum to begin with and the drain/tub is perfect.(no irregularities). Such perfect conditions just don't occur in nature. Again, the Coriolis effect is very very very weak at these scales and easy easily swamped out by other factors.

The only way you could get different direction spin under exactly equal conditions is if the water starts with near zero angular momentum to begin with and the drain/tub is perfect.(no irregularities). Such perfect conditions just don't occur in nature. Again, the Coriolis effect is very very very weak at these scales and easy easily swamped out by other factors.
But there is an effect, however weak, even at extremely small scales.

Would this not mean that if you had two similiar star systems created under similiar circumstances, but one in the upper hemisphere of a galaxy and another in the lower, that they would rotate in opposite directions?

DaveC426913
Gold Member
But there is an effect, however weak, even at extremely small scales.

Would this not mean that if you had two similiar star systems created under similiar circumstances, but one in the upper hemisphere of a galaxy and another in the lower, that they would rotate in opposite directions?
Are you looking for an answer in principle, or in reality?

Because in reality, any force is far overwhelmed. Thus, no effect.

Are you saying then that in principle this could be the case?

Is it possible that the Coriolis effect could be more prevalent in the void of space then it is here on Earth (ie, less encumbered by other forces)?

D H
Staff Emeritus
There is no real Coriolis force in space, or anywhere for that matter. The Coriolis effect is a fictitious force that arises from viewing things from the perspective of a rotating reference frame. When viewed from the perspective of an inertial frame, the "force" doesn't appear. We on the Earth prefer to use a rotating reference frame because such a viewpoint is very convenient in describing behaviors that are nearly co-rotating with the surface of the Earth.

Has this actually been studied?

Even if an effect is weak, it should be demonstrable statistically (given a large enough sample), presuming we have some means of making such measurements.

Moreover.. Say part of a rotating galactic dust-cloud collapses into a star with solar system. By conservation of angular momentum, how can it not end up rotating in the same direction as the galaxy was? There aren't any external irregularities to impose a greater force, so it does seem natural to expect most things to turn clockwise in the northern sky, and anti-clockwise in the southern sky, at least on average (leaving room for chaotic motions).

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russ_watters
Mentor
There is no real Coriolis force in space, or anywhere for that matter. The Coriolis effect is a fictitious force that arises from viewing things from the perspective of a rotating reference frame.
Yes, and in space, how could such a thing even manifest itself in principle? The only interaction between objects in space is gravitational. It isn't like they are all sitting on the same rotating solid object.

And Pilgrim, when you say "the galaxy" do you mean our galaxy? Our galaxy is a spiral galaxy. It is roughly planar. It doesn't have "hemispheres".

There is no real Coriolis force in space, or anywhere for that matter. The Coriolis effect is a fictitious force that arises from viewing things from the perspective of a rotating reference frame. When viewed from the perspective of an inertial frame, the "force" doesn't appear. We on the Earth prefer to use a rotating reference frame because such a viewpoint is very convenient in describing behaviors that are nearly co-rotating with the surface of the Earth.
Correct.

Relativistic Rotation: A Comparison of Theories
Robert D. Klauber
Foundations of Physics, Vol. 37, No. 2, February 2007

There is no real Coriolis force in space, or anywhere for that matter. The Coriolis effect is a fictitious force that arises from viewing things from the perspective of a rotating reference frame. When viewed from the perspective of an inertial frame, the "force" doesn't appear. We on the Earth prefer to use a rotating reference frame because such a viewpoint is very convenient in describing behaviors that are nearly co-rotating with the surface of the Earth.
But it is used to explain why winds and water go in different directions in Earth's hemispheres. Could the same calculations not be applied on a galactic scale? Could the same effects be seen on a galactic scale, involving planetary movement instead of winds?

As mentioned earlier, one would need a 'perfect' sink to witness the Coriolis effect on a small scale - could space not provide this 'prefect sink', with the gravitational well at the centre of our galaxy acting as the 'drain'?

The only interaction between objects in space is gravitational. It isn't like they are all sitting on the same rotating solid object.
Couldn't string theory and electric universe theory potentially contradict this statement?

And Pilgrim, when you say "the galaxy" do you mean our galaxy? Our galaxy is a spiral galaxy. It is roughly planar. It doesn't have "hemispheres".
Maybe 'hemispheres' isn't the right term, but there is an imaginary line which bisects our galaxy.

Relativistic Rotation: A Comparison of Theories

kthnx.

The reason that the earth has the "bathtub" effect of opposite direction of spinning in the northern and southern hemisphere, is because its surface has a different direction at each point. The hurricanes spin the same way, but we are looking at them from the other side.
(on both hemispheres, hurricanes spin in the direction that's closest to the direction that the earth spins in)
If we go north in the norhern hemisphere, we get closer to the earth's axis, hence conservation of angular momentum means that our rotation must speed up, so there is a coriolis force to the east.
If we go north in the southern hemisphere, we get further away from the earths axis, so there is a force to the west.
In a galaxy you do not have such a surface, so there is no reason to adopt our wierd set of coordinates.

Adopting a rotating reference frame for the galaxy seems natural, let's say north is along the galactic axis, east is in the direction of rotation, r is the distance to the center.
There will be a coriolis force, it will only be there if you move in the r direction and it will be the same everywhere.

D H
Staff Emeritus
Adopting a rotating reference frame for the galaxy seems natural, let's say north is along the galactic axis, east is in the direction of rotation, r is the distance to the center.
There will be a coriolis force, it will only be there if you move in the r direction and it will be the same everywhere.
What rotation? A galaxy is not a solid object. Stars closer to the galactic center have a much shorter orbital period than stars far from the center. There is no such that as a single galactic rotation rate. It seems much more natural to adopt an inertial reference system, and this is exactly what astrophysicists have done.

LURCH
In theory...
The Coriolis effect could almost certainly occur in space. Furthermore, our solar system would be the perfect testing ground because the axis on which all the planets orbit (the rotational axis of the sun) is roughly orthogonal to the axis of rotation for the Milky Way.

The in practice...
There would be no way of observing this effect, as all systems that are currently "above" the "Equator" of the Milky Way spend half of their orbit around the galactic center "below" that same Equator. So, nothing stays in one "Hemisphere" of the galaxy.

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D H
Staff Emeritus
What Coriolis effect? The Coriolis effect is solely a function of using a rotating reference frame. It is not real. We like to use a planet-fixed (i.e. rotating) frame to describe phenomena on the surface of the Earth (e.g. weather) because that is the natural frame for describing such phenomena. A consequence of this choice of reference frames is that we must introduct ficticious fources such as the Coriolis effect to make it look like Newton's laws still apply.

Moreover, what is this galactic rotating (note well: not accelerating) reference frame that would yield a Coriolis effect? The galactic reference frame used by astrophysicists is not a rotating frame. The International Celestial Reference Frame used by astronomers is not a rotating frame. Astrophysicists do not use a rotating reference frame to describe/model the galaxy because there is absolutely no reason to do so and a plethora of reasons not to do so.

DaveC426913
Gold Member
I'm not agreeing with the OP, but I think his question could use some clarification.

If the galaxy is, stars notwithstanding, a big cloud of dust and gas, will masses of dust and gas not be subject to similar forces as storms on Earth? If dust and gas tenuously held together by gravity is migrating through a part of the galaxy will it not be pulled into rotation due to similar forces?

Forget about whether it's called Coriolis, why would the cloud of gas and dust that is the galaxy not behave similar to the mass of the Earths' atmo?

LURCH
What Coriolis effect? The Coriolis effect is solely a function of using a rotating reference frame. It is not real. We like to use a planet-fixed (i.e. rotating) frame to describe phenomena on the surface of the Earth (e.g. weather) because that is the natural frame for describing such phenomena. A consequence of this choice of reference frames is that we must introduct ficticious fources such as the Coriolis effect to make it look like Newton's laws still apply.
One can odserve the Earth from any refference frame and the results would still be the same; hurricanes rotate in one direction in one hemisphere, and the opposite direction in the other hemisphere. Hurricanes do not form on the Equator, and those that pass over the Equator lose rotation and cohesion, and break up. These things happen for a reason. Coriolis Effect is not a ficticious force, but a very real set of interactions between moving air masses and the ground which cause the above-mentioned phenomina to occur. That is why it is not called the "Coriolis Force," but an "Effect."

I'm not agreeing with the OP, but I think his question could use some clarification.

If the galaxy is, stars notwithstanding, a big cloud of dust and gas, will masses of dust and gas not be subject to similar forces as storms on Earth? If dust and gas tenuously held together by gravity is migrating through a part of the galaxy will it not be pulled into rotation due to similar forces?

Forget about whether it's called Coriolis, why would the cloud of gas and dust that is the galaxy not behave similar to the mass of the Earths' atmo?
That's what I was getting at. A low-pressure system in Earth's atmosphere will begin rotating because it is inside a rotating sphere. So, one bit of the system is closer to the pole of the sphere, and therefore moving more slowly in the direction of the sphere's rotaion, than the other side. But this requires the low-pressure system to maintain a constant or near-constant lattitude. In Earth's atmosphere, the system can be held in place by the thick gasses that saround it. So it stays on one side of the Equator and picks up angular momentum via the Coriolis effect.

But in the very thin cloud of a rotating gallaxy, there is nothing to keep systems (like the Solar System) in one hemisphere. They all orbit the gallactic center at whatever slight inclination they may have, spending half their time above the equator and half their time below it. Additionally, there is no solid "surface" underneath these systems to cause frictional drag and set them spinning. There is also the fact that these systems are so small in comparison with the gallaxy that they really can't get any appreciable Coriolis Effect from its rotation (like bathtubs and kitchen sinks on Earth). So, the rotation of star systems within a rotating gallaxy is almost completely uneffected by gallactic rotation, and is strictly a function of whatever angular momentum was present in the initial gass cloud from which that star system formed.

DaveC426913
Gold Member
So, the rotation of star systems within a rotating gallaxy is almost completely uneffected by gallactic rotation, and is strictly a function of whatever angular momentum was present in the initial gass cloud from which that star system formed.
Exactly. That's what the OP was getting at. The systems formed from masses of dust and gas that may be affected by Coriolis-like forces from a rotating galaxy.

There is no such thing as a Coriolis "Force". It is only an "Effect" that is based purely on rotational motion. So yes in theory this EFFECT could be observed in any rotating system such as a galaxy. However for the reasons that LURCH explained, you most likely could not observe this effect occurring naturally on a Galactic scale.

I would like to bend the subject slightly. Forget solar system rotation, doesn't the whole galaxy look like its affected by Coriolis effect? It looks like a storm right.

I would like to bend the subject slightly. Forget solar system rotation, doesn't the whole galaxy look like its affected by Coriolis effect? It looks like a storm right.
This is easy to test with observation.

If our polar shift does indeed occur as a result of the passage of our solar system threw the galactic equator then the direction of stellar rotation for systems and bodies above the galactic equator should be the same for nearly all systems and bodies.

Therefor, we need to create a data set for 2 groups of stellar bodies; a northern group for all bodies above the galactic equator, and southern group for all bodies below the galactic equator.

If the passage of our solar system threw the galactic equator is the cause of this shift then there should be a statistically significant number of stellar bodies rotating in the same direction in each hemisphere respectively. This data set will, i believe, clarify this potential dynamic.

Chronos
Gold Member
I agree with Lurch, a coriolis effect exists in our solar system and galaxy. Is it significant? Probably not. I have observed the coriolis effect in high velocity rotating mechanical equipment, so I am a believer. It was not enough [barely] to require redesign, but, certainly food for thought.

This effect should be easily observable in the sky, has anyone seen it or does anyone have any access to the astronomical record of our galaxy?

Chronos