# I Orientation of the Earth, Sun and Solar System in the Milky Way

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1. Oct 10, 2017

### JDL1964

@fizixfan
A beautiful depiction of everything I've been taught over the years brought together very nicely... and yet it appears to be missing part of the "3D" aspect of motion. While you show the "orbital wobble" around the axis of the Sun and Earth, it's missing on the Moon (as well as the Moon's North Pole, a minor issue yet still incomplete), but on the bigger scale, you've not included the wobble on the Galactic North Pole. I cannot imagine that it would be totally stationary and locked when everything that it's comprised of isn't stationary at all, even if we don't yet know the amount of the angle of the galactic wobble (however small that may be). Also not shown is the effect of that wobble in regards to the path of the Sun around the Milky Way, or the effect that it would have on the Galactic Plane of the Milky Way itself. Perhaps a "thickening/thinning" of the path lines to show the "to/fro" of the motion that can't be shown with up/down pathing, and provide a 3D view of the Earth/Moon orbits? It all really simply depends on just how accurate you want it to be, but even if we don't know the numbers, we can show the motion with a "?", and let someone fill that in at some future date. I'm sure at some point, some mathematician will figure out ALL the numbers and win some kind of award for it, but since it takes 240Million years for a galactic revolution, it may be a while.

2. Oct 12, 2017

### fizixfan

I'm sure exactly what you mean by "orbital wobble," since it's not a standard term. Perhaps you mean rotational wobble, ie, precession. My diagram doesn't show precession, but it does show the relative inclination of the orbits of the moon, earth and sun, and the undulating path of the sun around our galaxy. Those circular arrows don't show "wobble" if that's what you mean - they just indicate the direction of rotation. Our solar system has a negligible effect on the axis of rotation of the Milky Way - it's just one of hundreds of billions of stars. It's hard to show everything in 3D in a 2D model. The orbits coming "out" of the diagram show the rotation arrows in front of and behind the axes of rotation.

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• ###### Ecllptic Plane & Galactic Plane (ESO) 11Oct2017.jpg
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3. Oct 12, 2017

### fizixfan

CORRECTION: To my post #42 above:

I'm NOT sure exactly what you mean by "orbital wobble"

4. Oct 13, 2017

### JDL1964

Okay, I'm terrible at getting my thoughts out. I know this, so please bare with me as I get stupidly simple in my thought process here (me, not you).
First, let me say that I had incorrectly seen your "direction of rotation" as the rotational wobble of the planet, which is why I wondered why you didn't show it on everything else. My bad. However, in response to your not quite understanding what I was referring to... It's much like the rotational wobble (i.e. precession) you're referring to, but delegated up and down to the various next level, then the next, then the next...etc. Singular precession, orbital precession (as objects orbit each other), Stellar percession (a system orbiting a star), galactic precession... ... ... see how the scale gets bigger and bigger?

Now for me to get REALLY stupid... If you'd like, you can let me know where I'm wrong in all this.

Let's say the Earth were all alone floating around in space with nothing else close enough to it to have any kind of gravitational effect on it what-so-ever. Thanks to its own internal gravitational torque, it would end up spinning around on its axis just as pretty as you please, like a top that never quits.... assuming that the mass and composition isn't a perfectly formed ball of iron too small to liquefy the central core, it should also begin going around in a little circle while it spins and the mass is constantly flung around 360 degrees. The same goes for the top/bottom of the Earth which would cause the tilt. So now we have a tilted, rotational and circular motion on this one Earth (a motion transition that can be shown with any decently spun top floating in a vacuum). There's the percession of motion with just one single Earth.

Now stick a Moon around that Earth. The Moon would have all of the same aspects as the Earth when it comes to motion, but now they begin to orbit each other. Due to the difference in mass between the two and the difference in the angular momentum and so on, they wouldn't orbit in a perfect plane or in a perfect circle (unless they had equal mass). They would circle each other and begin to go up and down on that plane just as your Suns path around the Milky Way shows... but this motion would be between the Earth and Moon. Up and Down, Left and Right, To and Fro in a never ending circular circle that in time would hit every angular degree possible and start all over again.
Now add in the Sun. A MASSIVE element that would bring a bit of stability to the motion of the Earth/Moon's orbital rotating dance. The Sun has its own polar axis and rotational motion, as well as it's own tilt and wobble just as the Earth and Moon do. The plane of motion would settle down for the Earth/Moon, but it would still go up and down on the Suns equilateral plane and therefore the orbit isn't perfectly circular around the Sun. This gives the Sun an orbital wobble to the rest of the bodies orbiting.

The Sun doesn't sit still in it's place just as the Earth/Moon combination, or even the Earth by itself doesn't. There's the "orbital wobble" I'm referring to. The not quite so circular path that everything ends up taking due to the forces of the gravitational torque that builds and builds as you add more and more. This motion isn't just applied in the top down view, but also on a side view as well which is why you get the up and down path of the Sun to the Ecliptic Plane of the Galaxy your drawing shows. Up and Down, In and Out, Left and Right... all motion in all directions all the time. Nothing is static. Of course once you get to a point of view large enough, then that motion becomes negligible, but it's still there. That's the 3D motion I was saying was too bad wasn't depicted. Of course nothing would be to scale, but when you're talking about orbits around galaxies, putting it to scale is impossible.

5. Oct 13, 2017

### fizixfan

https://en.m.wikipedia.org/wiki/Barycenter
The focus in my OP was to illustrate the “Orientation of the Earth, Sun and Solar System in the Milky Way,” so perturbations in multiple-body orbits were not considered.

6. Oct 15, 2017

### Dahook4444

Excellent diagram! Still not clear how we are able to distinguish the Sun's forward motion around the Galactic center from the forward motion of the "Orion Arm"? If we assume one rotation of Sun around Galactic center at 26K light year radius we are looking at a distance of 164K light years over say 226 million years. So one degree of forward motion would take approx. half a million years. Now math is not my strong point so happy to be "slapped down".
Also the "declination" cycle of Sun above and below the Galactic plane has been estimated at 70 millions years to complete.and this seems to be the most
Influential short-term cycle, so interesting to speculate on its cause. Within this cycle we get the Precession cycle of 26k years, as seen from the Earth which suggests constellations are moving with the Sun. Point I'm making is the time scales and distances are so vast how do we separate out observed fact from assumption.

7. Oct 17, 2017

### JDL1964

Barycenter!!! THAT's the word I was looking for! (slaps forehead). Anyway, as I was saying, I love your diagram... if you decide to do one that goes out to a larger scale (say... galactic?), I'm sure you would use 3D styled lines to show the to/fro motion as the bodies revolve around their barycenter. Can you imagine the detail that would have to be placed into that one?

8. Oct 17, 2017

### phyzguy

I get the impression from these discussions that you are picturing the orbit of the sun around the Milky Way as a closed curve. This is almost certainly not the case. Orbits in 1/r potentials like the solar system are closed curves, but in a potential like the potential of a galaxy, the orbits are almost never closed curves. This site discusses some of the complexities. In addition, the galaxy potential changes with time. So the sun's orbit around the galaxy center probably looks more like one strand in a bowl of spaghetti than a classical Keplerian orbit.

9. Oct 18, 2017

### JDL1964

@phyzguy
No such thing as a closed orbit (except in possibly extremely rare cases, and then only when greatly limiting ones viewpoint). Gravitational motion tends to eliminate that possibility from the beginning. Even limiting our view all the way down to the earth/moon orbit, we find that the moon is moving away from the earth just a tad bit every year. The Earth is moving away from the sun as well, and again, just a tad bit each year. Not enough to make any real difference in a thousand thousand lifetimes, but because that movement is there, the possibility of a closed orbit is impossible. Even the solar system doesn't end up back in the exact same place relative to the galaxy when it's completed an entire revolution. Expand the view to the local cluster, and any thought of any kind of closed orbit just goes right out the universal window. :)

10. Oct 21, 2017

### Dahook4444

One thing is very clear we are still not sure about the Structure of the Milky-way as no one has ever seen it from outside (see www.skyandtelescope.com article
Seeing Far side of Milky Way) Two spiral arms or Four? Gaia Mission also raises interesting questions about the trajectory of stars. Stars primary motion around the Galaxy would seem to be the result of the rotation of the Spiral arms in which they reside. The Gaia mission on the other hand would suggest that all stars have a secondary orbital trajectory within their host spiral arm i.e. Sun's 70 million year declination cycle. The apparent erratic trajectory of some stars would suggest collisions are probable so Solar system not closed and some researchers believe our Solar system is a "fruit salad" of captured planets and Red dwarf stars (Velikovsky). That would certainly better explain Venus environment than "Greenhouse warming".

11. Oct 21, 2017

### Janus

Staff Emeritus
The present model for the spiral arms is that they are caused by density waves moving through the galaxy independently of the orbits of the stars. Stars on the inner part of the galaxy orbit faster than the density waves move and those far out orbit slower. Thus stars move in and out of the spiral arms over time. The relative brightness of the arms is caused by the increased density causing greater star formation. By the time the stars formed in the density wave leave it, the bright massive stars have died, leaving only the cool dim stars with longer lifetimes. So the brightness of the spiral arms isn't about a difference in the number of stars in the spiral arms but rather that there is a greater population of young bright stars

12. Oct 31, 2017

### fizixfan

I agree that the solar system doesn’t come back to its starting place in its orbit around the galaxy. It’s in a sort of loose colloidal suspension with neighboring stars, gas clouds and other interstellar material, even passing through various spiral arms in its journey around the Milky Way. But comparing its orbit to a strand in a bowl of spaghetti is pushing the analogy a bit far, I think. I’d compare it to a molecule of milk in the very top layer of a stirred cup of coffee, but even that’s inadequate.

13. Nov 1, 2017

### phyzguy

Here is a recent paper on the arxiv about orbits in a potential with a bar like the Milky Way. I've pasted in Figure 3 Below, which shows the orbits over 1 Gy on
the left and 10 Gy on the right. I'll let you judge, but think my spaghetti analogy is apt.

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14. Nov 1, 2017

### fizixfan

The problem with a strand of spaghetti is that it's static, and doesn't convey a sense of motion. A strand of spaghetti can loop back in on itself, and follows no particular direction. Maybe a strand of spaghetti wrapped around a fork. I'm not a fan of the spaghetti strand model. If you're going for something that is static, maybe the tangled fishing line model or the ball of yarn model. I prefer the dynamic colloidal cream-in-coffee model.

15. Nov 1, 2017

### Drakkith

Staff Emeritus
Huh. It conveys a sense of motion for me. *shrug*

16. Nov 1, 2017

### fizixfan

This is getting seriously off-topic. In my original diagram, which took me many hours and a lot of research to complete, I wasn't thinking about whether or not spaghetti was an appropriate analogy.

I was thinking about how to portray the "Orientation of the Earth, Sun and Solar System in the Milky Way" in a 2-D diagram. It seems to please some people to pick things apart and dwell on small details.

17. Nov 1, 2017

### Drakkith

Staff Emeritus
My apologies if it seemed like I was picking apart your post. That certainly wasn't my intention.

18. Nov 1, 2017

### fizixfan

No problem! Cheers.

19. Nov 2, 2017

### sophiecentaur

I think you misinterpreted the reaction you got. When you introduce a useful contribution like your animation, you trigger a lot of thoughts in a lot of heads and you can expect all sorts of technical comments which can read like adverse criticism when they aren't. People (me too) tend to forget to compliment a contributor and that can be a bit off-putting to a newcomer to PF. (We are dealing with the Nerdy end of the market here and the niceties are often ignored; on balance, it works very well, though.)

20. Nov 2, 2017

### Drakkith

Staff Emeritus
Got a valid reference for that, sophie?