In building a three dimensional model of the solar system through time, the solar system barycentre inscribes a Z axis of movement around the galaxy.

What is the angle between this Z axis of solar system movement around the galaxy and the XY plane of the solar system planetary ecliptic?

The ecliptic is inclined at around sixty degrees to the galactic plane.
Here is a picture of the solar system, looking past the sun towards the galactic centre. Galactic plane horizontal. Orbits of the planets in blue. Movement of the sun pretty much leftwards, though rising a little.
Current coordinates of the galactic north pole in ecliptic coordinates are: latitude 29.81º, longitude 180.02º.

Grant Hutchison

Thanks very much Grant. Great picture, very informative. From this picture, the plane of the solar system passes through the centre of the galaxy. That makes sense since the Galactic Centre is on the zodiac line in Sagittarius. If anyone is able to help, I would be very grateful for answers to the following further questions.

1. Are many planetary systems aligned like ours, with their ecliptic plane including the galactic centre?

2. In the picture, does the leftward movement of the system spiral clockwise or anti-clockwise?

3. How fast is it? (or, what is the distance and period of the path of the sun around the galaxy?)

4. Is the upward component of the leftward motion due to the movement of the sun against the galactic plane?

5. Have the period and amplitude of this up and down galactic motion been worked out?

I doubt it. The alignment is happenstance, since it will disappear as the sun moves along its orbit.

I don't know about "spiral". The sun's movement is clockwise around the galaxy when viewed from galactic north.

There are various estimates. The Local Standard Of Rest is moving at around 200 km.s^-1: that's circular velocity for our distance from the galactic centre. Relative to the LSR, the sun has its own velocity: 14 km.s^-1 faster around the galaxy, inwards towards the galactic centre at 10 km.s^-1, and towards galactic north at 7 km.s^-1. (Figures from Frank Bash; there are other estimates.) The sun will take about 240 million years to go once around the galaxy.

The sun is north of the galactic plane at present, and moving farther from it.

They have. The period is about 65 million years. The amplitude is about 200 light-years either side of the galactic plane.

Grant Hutchison

Thanks for that Grant. Your figures confirm my own research and strikes a body-blow to the 2012 galactic plane crossing, scare-mongers.

Many thanks for these excellent answers Grant. Some points of clarification if I may
Why is that? If you think of the solar system as like a snowplough pushing its way around the Milky Way, the blade has pitch of sixty degrees but zero yaw. Would continuing this setting mean the ecliptic will stay aligned to the galactic centre?
What I was asking is, if you take your picture, which is a static shot of the solar system against the galaxy at one moment in time, and extend it through time by depicting the planets as spirals around the cylindroid formed by the movement around the galaxy, then do the planets also go clockwise viewed from solar north?Great! By my further calculation this means we go 1500 trillion kilometres per galactic cycle! These figures show the sun moves over six billion kilometres per year. So November 4 next year we will be 6.3 billion kilometres (42 AU) further on. (I'm sure that AU figure was the answer to something). Over the Jupiter 11.85 year cycle the system will have moved 75 billion km. Jupiter's orbital diameter of 1.6 billion km depicted as a spiral would loop back to itself with a period almost 100 times the spiral diameter. Thanks Grant, am I right to understand the unit of the 65 MY period is two halves of a sine wave, so the period is the time taken to return to the same position of a wave function? Does this mean the sun spends an equal amount of time north and south of the galactic plane? For example, over the 65 million years since the dinosaurs, has the sun been equally north and south of the galactic plane?

But to continue that setting you'd need a force to precess the plane of the ecliptic at exactly the (variable) angular rate of the sun's orbit around the galaxy.

The planets go anticlockwise. And they describe a helix, not a spiral.

The 65-million-year period is the cycle time of the sine wave, yes. So the sun spends equal time north and south in any period of that duration.

Grant Hutchison

Grant, I do appreciate your informative explanations. I am just trying to get my head around a simple dynamic model for the solar system, and all these angles and details are essential. Apologies if my questions are basic. I am always eager to see references.

So far we have the SSB buzzing along at LSR of ~200km.s-1, plus 14km.s-1 as we depart from the great ring, planets forming anticlockwise helixes with SSB as their Z axis, Earth annual return distance 42 AU, the leading edge of the system pointed down 60 degrees and with zero yaw against galactic centre. So the solar system keeps in a precessing plane with the universe while it orbits the galaxy? For a minute I had in mind it spinning on a string entrained from the galactic centre. With the apparent movement of the galaxy around the earth over 240 million years, the galactic centre must drift north or south across the ecliptic every 120 million years.

Is the galactic centre ever near one of the earth's celestial poles?

If the plane of the zodiac against the galaxy is fixed like the tilt of the orbit of the earth against the sun, does this mean there are 'seasons' in the galactic year, and we are now at an equinox, just as the sun crosses the equator at the equinox?

On this model, in 'summer/winter' in 60 million years, will the galactic centre have moved into the south celestial hemisphere or the north?
Thank you I earlier corrected myself from spiral to helix, I just use spiral as a simpler term - knowing it is less accurate! Makes me think of a millipede crawling through space.
Does this mean our whole spiral arm is flapping up and down with this period?

I haven't found an accessible copy of Frank Bash's original paper on-line. The figures I've given you come mainly from him, via Henbest and Couper's The Guide To The Galaxy. (Recommended, though now just a little dated.)

The plane of the solar system will stay in the same orientation unless some force acts to change it. I certainly doubt if it will sail around keeping itself edge-on to the galactic centre. So a very long-lived observer would see the galactic centre cycle from ecliptic north to ecliptic south and back again, yes.

In 8,000 years or so, the celestial poles will have precessed so that they're lying close to the galactic plane, though not actually on it. That will repeat every 26,000 years. So we could imagine that there might come a time, quarter of a galactic orbit from now, when precession would bring one pole close to the galactic centre.

Certainly the position of the galactic plane in the sky goes through cycles, with the precession period and the galactic orbital period.

From my diagram, the galactic centre looks to be moving south of the ecliptic at present. It's already in the southern celestial hemisphere.

No, for several reasons. The arm is a statistical structure: just a density wave that doesn't share the motion of its component stars. And the arms are delineated by bright, short-lived stars which pass through their entire main sequence career in a few million years, far shorter than the vertical oscillation period. I'm also not sure if the vertical period is the same for all amplitudes of oscillation (like a pendulum), or if we can expect a mixture of oscillation periods.

Grant Hutchison

i was trying to figure this out my self, glad you asked this question robert,still not sure i understand this fully . but this is a great start
thx guys

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