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

[fizixfan]

I've been tinkering with a few diagrams in an attempt to illustrate the motion of the solar system in its journey around the Milky Way. I also wanted portray how the celestial, ecliptic and galactic coordinate systems are related to each other in a single picture. Note: in the Celestial, or Equatorial system, the Celestial North Pole (an extension of the Earth's axis of rotation), uses the default setting of North as "up." The Ecliptic and Galactic also use North as "up" with reference to the Celestial North Pole. Some people say that in space there is no such thing as "up" or "down," but in determining the position of a celestial object (e.g., declination and right ascension of a star or deep-sky object) is DOES matter.

Please have a look at these diagrams and feel free to comment on any errors, or make suggestions as to how I could make them better. I drew these images, but anyone is free to re-use them without restriction.

Figure 1 shows the motion of the Earth and Sun around the Milky Way. The solar system is actually well within the galactic disk, which is about 1,000 light years thick. The sun and the planets that circle it is roughly 50 light years above the galactic plane, and passed northward through it about 3 million years ago in its undulating path around the galactic center. Note: this diagram is not to scale. The northernmost excursion of the solar system takes it about 250 light years above the galactic plane. This means it would only subtend an angle of about 0.55° relative to the galactic center.

Figure 1. Motion of Earth and Sun around the Milky Way

Figures 2. and 3. show the orientation of the Earth, Sun & Solar System in the Milky Way - similar diagrams, just presented in different ways.

Figure 2. Orientation of Celestial, Ecliptic and Galactic Poles and Planes

Figure 3. Orientation of astronomical coordinates projected on the Celestial Sphere.

The angle between Celestial Equator (an imaginary plane passing through the Earth's equator) and the Ecliptic Plane (an imaginary plane extended through the Sun's equator) is 23.4°. The angle between the North Celestial Pole (an imaginary line extending through Earth's axis of rotation) and the North Ecliptic Pole (an imaginary line extending through the Sun's axis of rotation) is the same - 23.4°. This is the familiar value for the "tilt" of the Earth in its path around the Sun.

The angle between the Ecliptic Plane and the Galactic Equator (an imaginary plane passing through, and parallel to, the disk of the Milky Way) is 60.2°. The angle between the North Ecliptic Pole and the North Galactic Pole (an imaginary line extending through the Milky Way's axis of rotation) is also 60.2°.

The angle between the Celestial Equator and the Galactic Equator is 62.9°, as is the angle between the North Celestial Pole and the North Galactic Pole.

These three angles = 23.4°, 60.2° and 62.9° cannot be shown or calculated in two dimensions, because they represent separate planes which do not intersect at a common point. If you look at Figure 3, you can see that this is so.

References:
https://en.wikipedia.org/wiki/Celestial_coordinate_system#Galactic_system
https://www.eso.org/public/news/eso0932/
http://www.engineeringanddesign.com/1/054.htm

 

[phyzguy]

Nice! I didn't check the accuracy, but they look reasonable. My only comment is that in the first diagram, I would change "Celestial Plane" to "Celestial Equator" as you have done in the other two diagrams.

 

[Janus]

I'd just make one small point. In your first diagram, it appears as if you are showing the Moon's orbit as being on the same plane as the Celestial plane/equator, where, in reality, it is inclined by ~5 degrees to the ecliptic (~18 degrees to the Celestial equator).

 

[fizixfan]

Nice! I didn't check the accuracy, but they look reasonable. My only comment is that in the first diagram, I would change "Celestial Plane" to "Celestial Equator" as you have done in the other two diagrams.

Thanks phyzguy, and appreciated. I called it Celestial Plane to be consistent with the terms Galactic Plane and Ecliptic Plane I used in this diagram. But you're right - it should be referred to as the Celestial Equator - I will adjust accordingly. See image attached to my following reply to Janus.

Cheers.

 

[fizixfan]

I'd just make one small point. In your first diagram, it appears as if you are showing the Moon's orbit as being on the same plane as the Celestial plane/equator, where, in reality, it is inclined by ~5 degrees to the ecliptic (~18 degrees to the Celestial equator).

Thanks Janus - I knew the moon's orbit was inclined relative to Earth's equator, but I didn't know it was inclined TOWARD the ecliptic. Interesting! I've included your suggestion in my diagram, which also includes phyzguy's suggestion. Really appreciate the input, hope this diagram isn't getting too busy.

 

[picnics]

quote: I drew these images, but anyone is free to re-use them without restriction.

Thanks for sharing this great diagram!

quote: feel free to comment on any errors, or make suggestions as to how I could make them better

The definition of an ellipse is that it has 2 focus points,
therefore the the Sun is not at the center of the Earth's elliptical orbit.
The direction of the "Super Galactic Center"
would be a perpendicular line to the Earth's orbit, at about October 11.

 

[fizixfan]

The definition of an ellipse is that it has 2 focus points,
therefore the the Sun is not at the center of the Earth's elliptical orbit.

Thanks for your input. Yes, the Earth's orbit around the Sun is elliptical, but it's very nearly (97%) circular. Earth's apogee distance from the Sun is 152.1 million km, and its perigee distance is 147.1 million km. The orbit is shown to scale in the diagram below. Looks much like a circle, doesn't it?

The Earth-Sun system orbits a common center of mass called the barycenter. But because the Sun is so much more massive (99.9% of the mass of the entire solar system), the Earth-Sun barycenter is only about 449 km from the center of the Sun.

The direction of the "Super Galactic Center"
would be a perpendicular line to the Earth's orbit, at about October 11.

"Super Galactic Center" is not an astronomical term, as far as I know. If you mean the Galactic Center, I still have trouble visualizing what you mean by "a perpendicular line to Earth's orbit." A diagram might help.

 

[Dr Wu]

Looking at the Sun's direction of travel arrow on fizixfan's 'Motion of Earth & Sun around the Milky Way' diagram, does this mean then that the solar system is orbiting the Galaxy in a clockwise direction? Also, which hemisphere of Earth's is (mostly?) facing the direction the solar system is taking during its orbit round the galactic disc? North or South? Or do they each take turns during the course of a terrestrial year? I can't quite put it all together it somehow.

 

[fizixfan]

Looking at the Sun's direction of travel arrow on fizixfan's 'Motion of Earth & Sun around the Milky Way' diagram, does this mean then that the solar system is orbiting the Galaxy in a clockwise direction?

The short answer is yes, it is. In astronomy, there are conventional means for defining the positions and locations of celestial objects. The three most commonly used are the Celestial Coordinate System (with Earth as the primary point of reference), the Ecliptic Coordinate System (with the Sun as the primary point of reference) and the Galactic Coordinate System (Sun at center, with the primary direction aligned with the approximate center of the Milky Way galaxy).

In all three of this systems, Earth's North Pole is pointing "up" (you have to start somewhere). So in this frame of reference the Earth spins counterclockwise (CCW) on its axis, and orbits around the Sun in a CCW motion. The Sun also spins CCW on its axis. But the Solar System is moving clockwise in its orbit around the Milky Way. A lot of illustrations you'll find on the internet get this last part wrong, and if it's pointed out to them, many of them will say, "It doesn't matter, there is no up or down in space." That's true, but if does matter if you're using any kind of astronomical coordinate system.

Also, which hemisphere of Earth's is (mostly?) facing the direction the solar system is taking during its orbit round the galactic disc? North or South? Or do they each take turns during the course of a terrestrial year?

That's an interesting question. If you look at my diagram below, and observe the yellow arrow pointing toward the North Celestial Pole - that is aligned with the Earth's axis of rotation. You'll see that the Earth's northern hemisphere is inclined toward (facing, or "leaning into") its direction of motion around the galactic disk.

 

[Dr Wu]

Thanks, fizixfan. Speaking as an amateur stargazer, the Earth's orientation with respect to the Milky Way has always been something of a puzzle to me. But no longer!

 

[rbelli1]

The definition of an ellipse is that it has 2 focus points,

These two points can be the same and we usually call that a circle. Just like a rectangle with length and width equal is often called a square. The more specific figure still satisfies the definition of the more general figure. This does not apply here but may in other examples of orbits.

BoB

 

[rootone]

Looking at the Sun's direction of travel arrow on fizixfan's 'Motion of Earth & Sun around the Milky Way' diagram, ... does this mean then that the solar system is orbiting the Galaxy in a clockwise direction?

Yes if you are looking at the Milky Way from a point of view above it's North pole.
If you are viewing from below the South pole, the orbit of the solar system appears to be the opposite direction.

 

[Dr Wu]

Thanks for the info. Just one other question, though: I've since learned that the solar system is moving towards a point in the Milky Way presently marked by the 4th magnitude star, Lambda Hercules.* This being so, and to give a better idea about the trajectory of the solar system, at which point in the heavens does the solar system appear to originate from? I assume this point probably lies somewhere in the Southern Hemisphere - if only because the constellation of Hercules is in the Northern Hemisphere, but I have no proof of this. PS. I've tried to find out via Google, but despite my best efforts all I get are responses that have little or no bearing on this question.

*There are several variations concerning this location, but Lambda Hercules still appears to be leading the pack.

Note: I've since found out from Wikipedia that the 'solar antapex' is near the star, Zeta Canis Minoris! I could delete this query of mine, but I'll include it on this thread just in case others may wish to know the answer to this admittedly obscure question. Many thanks!

 

[chasrob]

Excellent renderings. Figure 3 reminds me of the illustrated The Astronomical Companion by Guy Ottewell.

 

[Dr Wu]

Just another last thought: does the Sun have anything corresponding to a 'pole star' - north or south? I mention this because if the Sun (and the solar system) is truly heading towards Lambda Hercules, that appears to conflict with the orientation of Earth's own axis (there being a whopping 65 degree difference in declination between Polaris and Lambda Hercules, one which Earth's 23.5 degree axial tilt doesn't appear to address). Or is the plane of the solar system moving at an oblique angle with respect to the centre of the Milky Way? If so, I'm still curious to know where the solar 'north pole' is orientated. My apologies for refusing to let this issue die of natural causes.

 

[Janus]

Just another last thought: does the Sun have anything corresponding to a 'pole star' - north or south? I mention this because if the Sun (and the solar system) is truly heading towards Lambda Hercules, that appears to conflict with the orientation of Earth's own axis (there being a whopping 65 degree difference in declination between Polaris and Lambda Hercules, one which Earth's 23.5 degree axial tilt doesn't appear to address). Or is the plane of the solar system moving at an oblique angle with respect to the centre of the Milky Way? If so, I'm still curious to know where the solar 'north pole' is orientated. My apologies for refusing to let this issue die of natural causes.

It points to the middle of Draco. The closest object I could find to that point is NGC 6543, which is the Cat's Eye nebula.

 

[Bandersnatch]

I mention this because if the Sun (and the solar system) is truly heading towards Lambda Hercules, that appears to conflict with the orientation of Earth's own axis (there being a whopping 65 degree difference in declination between Polaris and Lambda Hercules, one which Earth's 23.5 degree axial tilt doesn't appear to address).

What's this angle?

 

[Imager]

I’m not following the curved (yellow) path of Sun around the Galactic Plane (blue). I would have thought the sun’s path though the galaxy would be on the same plane or tilted. What would cause the sun to “rise and fall” relative to the galactic plane?

 

[Bandersnatch]

I’m not following the curved (yellow) path of Sun around the Galactic Plane (blue). I would have thought the sun’s path though the galaxy would be on the same plane or tilted. What would cause the sun to “rise and fall” relative to the galactic plane?

Since Milky Way isn't a 0-thickness disc, any given new star will be born either above or below the plane bisecting the galaxy. This results in a component of gravitational attraction pointing normal to the galactic plane due to all the matter in the disc pulling the star in.
If the star was born above, it'll be pulled down, pass the middle point (where gravitational forces will be purely radial), and overshoot on the other side, where opposite direction of gravity will again pull it into the disc, which it again overshoots. And so on.
As such, it's not much different than a pendulum.

 

[Imager]

Since Milky Way isn't a 0-thickness disc, any given new star will be born either above or below the plane bisecting the galaxy. This results in a component of gravitational attraction pointing normal to the galactic plane due to all the matter in the disc pulling the star in.
If the star was born above, it'll be pulled down, pass the middle point (where gravitational forces will be purely radial), and overshoot on the other side, where opposite direction of gravity will again pull it into the disc, which it again overshoots. And so on.
As such, it's not much different than a pendulum.

Got it, thank you! Would this "pendulum" motion be common for most stars in a spiral galaxy like the Milky Way?

 

[Imager]

@https://www.physicsforums.com/members/fizixfan.506800/ Great Diagram!

 

[Bandersnatch]

Got it, thank you! Would this "pendulum" motion be common for most stars in a spiral galaxy like the Milky Way?

All stars, more like. Just to a varying degree.

 

[rbelli1]

All stars, more like. Just to a varying degree.

And even if a star is born perfectly on center it will be perturbed out of true in very short order by other masses it interacts with.

BoB

 

[Uterr]

What is the angle between axis of the ecliptic and radius of the Galaxy? Exact 90 degrees?

 

[phyzguy]

What is the angle between axis of the ecliptic and radius of the Galaxy? Exact 90 degrees?

No, why should it be? They are just random orientations. Look at Figure 2 in Post #1 from this thread. It looks like the angle you are asking about is 60.2 degrees.

 

[Uterr]

60.2 is the angle between ecliptic and plane of the Galaxy. I am asking about the angle between radius of the Galaxy and axis of the ecliptic. The radius which connect center of the Galaxy and Sun. From many pictures this is 90 degrees but there is no information about that.

To be more precise - what is the angle between axis of the Galaxy projected on the plane of the Galaxy and the radius of the Galaxy that connects center of the Galaxy and Sun.

 

[Bandersnatch]

What is the angle between axis of the ecliptic and radius of the Galaxy? Exact 90 degrees?

96 degrees.

 

[Uterr]

Astonishing! Thank you. What is the source of this information?

Is it true that axis of the ecliptic stays still like a gyroscope and therefore this angle will change over the movement around the Galaxy?

I see that this angle is now in increasing mode. Am I correct?

 

[Bandersnatch]

What is the source of this information?

The celestial coordinates to the X-ray source Sgr A identified as the supermassive black hole at the centre of our Galaxy are known (~18h RA, ~-29 dec). The axis of Earth's rotation happens to be angled in such a way w/r to the ecliptic, that it's just a matter of adding its inclination (~23 degrees) to get the 6 degrees between the ecliptic plane and the galactocentric radial direction (or 90+6 if you want an angle with the normal to the ecliptic).
Best seen if you launch some planetarium software (I recommend Celestia) and turn on galactic, ecliptic, and celestial coordinate grids.

Is it true that axis of the ecliptic stays still like a gyroscope and therefore this angle will change over the movement around the Galaxy?

I see that this angle is now in increasing mode. Am I correct?

That's also my understanding.

 

[Janus]

Astonishing! Thank you. What is the source of this information?

To add to Bandersnatch's reply, here's a screen shot taken from the Worldwide Telescope software. The blue grid are the galactic coordinates, where (0,0) marks the center of the galaxy. The white grid are the ecliptic coordinates, with the ecliptic marked out 260, 270, 280, etc. Note that the ecliptic crosses the plane of the galaxy ~6 degrees from the galaxy center coordinates.

 

[Uterr]

I made a mistake in my 'precision':

To be more precise - what is the angle between axis of the Galaxy projected on the plane of the Galaxy and the radius of the Galaxy that connects center of the Galaxy and Sun.

Should be:
To be more precise - what is the angle between axis of the ecliptic projected on the plane of the Galaxy and the radius of the Galaxy that connects center of the Galaxy and Sun.
(can't edit post now)

Anyway thank you for understanding and answers!

 

[Uterr]

I made a sketch about this angle (lets hope it's correct;)

 

[Dr Wu]

All this would be wonderfully easy to visualise in 3D, of course

 

[Delphinus]

Hello there! Thanks for the interesting conversation, I have another question:

The solar apex has in consideration the movement of the surrounding context (respect to the so called local standard of rest). Because of that, it does no say what direction the sun is really going in respect to the milky way center.

So what is the direction of the solar system irrespective of the local standard of rest? I'd say it should be near 90º from the center of the Galaxy (because the solar system should be moving over the tangent), so somewhere near Deneb.

Thanks

 

[fizixfan]

Excellent renderings. Figure 3 reminds me of the illustrated The Astronomical Companion by Guy Ottewell.

I redrew this (Figure 3 from my OP) from an illustration I found in the Wikimedia Commons https://commons.wikimedia.org/wiki/File:Ecliptic_equator_galactic_anim.gif
It was one of the best visualizations of the relative orientations of the Celestial Equator, Ecliptic Plane, and Galactic Plane that I could find anywhere. Figure 2 was an attempt to show the angles between the Celestial, Ecliptic and Galactic North Poles and their respective planes. This is something that can't be done by simply adding or subtracting say, the angle of the Celestial Equator relative to the Ecliptic Plane (23.44°) and the angle of the Ecliptic Plane relative to the Galactic Plane (60.19°), to get the angle of the Celestial Equator relative to the Galactic Plane (which is 62.87°). You need spherical trigonometry for that, because the three planes don't intersect at a single point .

Oddly enough, what started me off on this whole quest many years ago was that I wanted to know the angle between the Earth's axis of rotation (Celestial North Pole) and the Galactic Plane. Turns out it is 27.13°.

 

[fizixfan]

The solar apex has in consideration the movement of the surrounding context (respect to the so called local standard of rest). Because of that, it does no say what direction the sun is really going in respect to the milky way center.

So what is the direction of the solar system irrespective of the local standard of rest? I'd say it should be near 90º from the center of the Galaxy (because the solar system should be moving over the tangent), so somewhere near Deneb.

According to Wikipedia, the Solar Apex refers to the direction that the Sun travels with respect to the mean motion of material in the Milky Way in the neighborhood of the Sun. I find these terms confusing, and don't use them much. But you can look here for more info: https://en.wikipedia.org/wiki/Solar_apex and https://en.wikipedia.org/wiki/Local_standard_of_rest

Basically, these terms refer to the "local motion" of the Sun with respect to its neighboring stars. The speed of the Sun towards the solar apex is about 20 km/s. The solar apex is located in the constellation of Hercules, southwest of the star Vega. So it's closer to Vega than Deneb.

However, the Sun and its neighboring stars are collectively moving around the center of the Milky Way in a clockwise motion (with Galactic North as "up") at about 230 km/s. This is perhaps what you mean by "the direction of the solar system irrespective of the local standard of rest."

The Sun is roughly 50 light years above (north of) the galactic plane, and passed northward through it about 3 million years ago in its undulating path around the galactic center. It might help to think of the stars in our galaxy as a kind of colloidal suspension, with the individual particles jostling each other randomly, but still moving around a common center.

 

[Delphinus]

However, the Sun and its neighboring stars are collectively moving around the center of the Milky Way in a clockwise motion (with Galactic North as "up") at about 230 km/s. This is perhaps what you mean by "the direction of the solar system irrespective of the local standard of rest."

Yes, but you did give any hint on the present direction of the sun in that "clockwise motion (with Galactic North as "up") at about 230 km/s"!

That direction should not vary much in our current life-span, as it turns very little, only 360º / (~230* 10^6) years = ~1,56 * 10^-6 degrees per year.

I think it is it should not be difficult to assess this direction (I've given my hunch) and, at least for me, it's much more interesting than the "solar apex" direction, because it's not so "local"!

 

[fizixfan]

Yes, but you did [sic] give any hint on the present direction of the sun in that "clockwise motion (with Galactic North as "up") at about 230 km/s"!

That direction should not vary much in our current life-span, as it turns very little, only 360º / (~230* 10^6) years = ~1,56 * 10^-6 degrees per year.

"Present direction" is a pretty vague term. It seems you meant "degrees per year," which refers more to a rate than a direction. In any case, it appears you have answered your own question.

 

[Delphinus]

"Present direction" is a pretty vague term. It seems you meant "degrees per year," which refers more to a rate than a direction. In any case, it appears you have answered your own question.

Lapsus calami: *didn't

Present direction in respect to the centre of he galaxy, if you care to understand; the direction the sun when considering it's the velocity of "about 230 km/s" which you've mentioned. Doesn't seam a vague term.

Last but not the least, I've only given my hunch, which is open for discussion. I wouldn't ask if I had the answer.

 

[Bandersnatch]

If I understand the conventions right, the stated direction of orbital motion is exactly at 90 degrees to the galactocentric radial direction, and that's what LSR motions are measured against.
So it's a bit ahead of Deneb:

If you want the 'real' direction of travel in galactic-rest coordinates, just add the velocity vectors w/r to the LSR.

By the way, I don't think the 20 km/s value and direction given by Wikipedia is a good one. At the very least it shouldn't be taken as anything more than a first approximation. The source for this value given in the article does not seem to actually have it, and in any case it's from 1993. Recent papers give a rather wildly varying (approx. 5-15 km/each component) velocity estimates (see here: https://arxiv.org/abs/1411.3572, including the referenced values).

The combined motion should be in the direction of somewhere around Lyra-Cygnus, and any more accuracy than that doesn't seem justified at the present time.

 

[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.

 

[fizixfan]

Thanks for your kind words.

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.

 

[fizixfan]

CORRECTION: To my post #42 above:

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

 

[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.

 

[fizixfan]

Check out this link:
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.

 

[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.

 

[JDL1964]

Check out this link:
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.

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?

 

[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.

 

[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. :)

 

[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 http://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".