Question: Orientation of Solar System to Galactic Plane

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Question: Orientation of Solar System to Galactic Plane
Posted by davidh on Saturday, February 09, 2008 5:52 PM

A number of years ago I read somewhere that the plane of the solar system is oriented around 90 degrees to the galactic plane.  That can't be right -- the geometry just doesn't work.  So, how is the plane of the solar system oriented to the galactic plane?

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Posted by Centaur on Saturday, February 09, 2008 6:10 PM

Welcome to the discussion group, davidh.

 

Actually the two planes intersect at an angle of about 60°.

 

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Posted by davidh on Saturday, February 09, 2008 6:34 PM

But that would make the central regions of the galaxy only visible from one hemisphere, likewise the outer regions would be visible only to the other hemisphere.  Perhaps it is the yaw that is 60 degrees, but I would think the pitch would be fairly close to the galactic plane.

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Posted by Centaur on Saturday, February 09, 2008 7:53 PM

The central region of the galaxy is in the direction of the constellation Sagittarius and not far from Scorpius.  It is near them that the plane of the galaxy intersects the ecliptic (plane of Earth’s orbit) at an angle of about 60°.  If the planes were nearly parallel, then we would see the Milky Way running through all of the constellations of the zodiac. 

 

Picture a summer evening while the region between Sagittarius and Scorpius is crossing your southern meridian.  The ecliptic would appear parallel to the horizon.   You would observe the Milky Way sweeping upward at an angle of about 60° to the ecliptic.

You mention the Earth’s hemispheres, but they are separated by the Earth’s equatorial plane, not the ecliptic or galactic planes.  The equatorial plane currently intersects the ecliptic plane at more than 23°.  In the current era, the center of the galaxy is visible from the Earth’s South Pole and not the North Pole.  That will eventually reverse due to precession.  But in either case, observers on most of the Earth’s surface experience periods of the day during which the galactic center is above the horizon. 

 

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Posted by avionna on Sunday, July 04, 2010 5:59 AM

Hello and many thanks for useful explanation, however.....as a picture tells a thousand words, and rather than re-inventing the wheel,  does anyone know of any website which would display the Earth's tilt and orbit within Solar System, within the Solar System's tilt and orbit around  MW,  in one diagram  ?

If at all possible a winter and a  summer  view for Northern Hemisphere  and same for Southern Hemisphere.

Many grateful thanks, Avionna

 

H.D.  Thoreau :  "  Why should I feel lonely !  Isn't our planet in the Milky Way ?  "

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Posted by chipdatajeffB on Sunday, July 04, 2010 6:46 AM

A good explanation by James B. Kaler is here. His book The Ever Changing Sky has diagrams that will help, but I haven't found similar diagrams online.

The illustration below (from the European Southern Observatory) dipicts the plane of the Solar System inclined 60 degrees relative to the plane of the Milky Way. It certainly is not to scale, and it shows the Sun centered in the Milky Way (which it certainly is not).

A photo-realistic interpretation of these alignments is not possible, because the disc of the Milky Way is thousands of times thicker than the Solar System is wide and the diameter of the Milky Way 50,000 to 100,000 times that of the Solar System.

So, the only accurate thing about the image is the rough angle between the two planes ...

A modern celestial globe is often clear plastic, with the earth depicted as a ball in the center and the stars, the ecliptic, and the band of the Milky Way shown on the outer clear sphere. The one shown below is an illuminated world globe that when illuminated in a darkened room shows the band of the Milky Way (the cross-hatched pattern) against the pattern of stars and constellations we call the 'celestial sphere' ...

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Posted by Centaur on Sunday, July 04, 2010 2:05 PM

It might be noted that planets revolve around the Sun in a somewhat retrograde direction relative to that of the stars’ movement around the galactic center.  That means what I earlier called a 60° intersection of the ecliptic with the galactic plane might more accurately be described as 120°. 

 

The IAU designates a point in the northern celestial hemisphere in Coma Berenices at RA 12:51.4 & Dec N 27°07’ (J2000.0) as the North Galactic Pole.  However, due to the generally retrograde motion of the galaxy relative to the Earth’s rotation, that point on the celestial sphere might be better described as the South Galactic Pole.

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Posted by DaveMitsky on Sunday, July 04, 2010 3:11 PM

A diagram showing the solar system's orientation with respect to the Milky Way can be seen here.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by chipdatajeffB on Sunday, July 04, 2010 5:07 PM

Now THAT is cool! Thanks, Dave!

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Posted by avionna on Monday, July 05, 2010 4:26 AM

 

Many grateful thanks for all the replies - it all makes a lot of differences to being able to  " visualise " for explaining........... without the hands going in all directions.

Cordialement

Avionna

(Any more info in that style will be welcome.)

H.D.  Thoreau :  "  Why should I feel lonely !  Isn't our planet in the Milky Way ?  "

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Posted by chipdatajeffB on Friday, July 16, 2010 2:16 PM

A comment Dave Mitsky made in a reply to another thread today, made me recall that an image showing the band of the Milky Way along with the zodiacal band would show this relationship. The link in the previous sentence is to an excellent Web page, with images and an illustration, by Doug Zubenel.

Here's an all-sky image by Laurent Laveder :

 

The Milky Way extends from upper left of center to lower right. The zodiacal band is fainter, extending from just right of center at top, to lower left (about 7 o'clock).

The zodiacal band is sunlight reflecting from dust in the plane of the Solar System, and extends about +/- 16 degrees either side of the path of the Sun through the sky (hence, it brackets the plane of the Solar System).

In this photo you can clearly see the angle between the starry band and the dusty band.

 

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

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Posted by DaveMitsky on Friday, July 16, 2010 2:36 PM

Thanks for posting that, Jeff.  I'd seen Doug's image before but Laurent's was new to me.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by chipdatajeffB on Friday, July 16, 2010 2:38 PM

One good idea begets another ... Smile,Wink, & Grin

Laurent's Web site is here. If you click on the Search box ("rechercher") and enter "Zodiacal" you'll find several dozen nice images of the zodiacal light and zodiacal band.

Edit: Oops! Thanks, Oliver ... I fixed it!

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

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Posted by Oliver Tunnah on Saturday, July 17, 2010 11:21 AM

 Jeff, that just links to the image again.

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Posted by avionna on Saturday, July 17, 2010 11:57 AM

Hi, thanks again, many good info  since my question.

Does anyone know of a constructed diagram with 4 intersecting orbital plane : MilkyWay, Sun, Earth ,  Moon.

I have tried a mixture of words, a change of order of words in Google  but I only have found some websites with only 2 planes  and  I would like the "grand encompassing " view in one picture.

Many thanks

Cordialement

Avionna

H.D.  Thoreau :  "  Why should I feel lonely !  Isn't our planet in the Milky Way ?  "

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Posted by adaaam007 on Saturday, July 17, 2010 12:25 PM

 

is there anyone who can help me here? i have some questions
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Posted by chipdatajeffB on Saturday, July 17, 2010 12:50 PM

Sure, there are lots of helpful folks here. Did you have a question about this particular topic, or some other question? If about something different, look for an existing topic that is nearer to your subject and ask away in that discussion area.

Welcome!

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

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Posted by chipdatajeffB on Saturday, July 17, 2010 12:59 PM

Well, that's not precisely possible, since orbital motions are rather complex and in systems of multiple bodies the orbital planes precess ... so, a given diagram would be precisely accurate for only a given moment in time.

At the largest abstraction level, the image of the Milky Way and our Solar System's zodiacal band pretty much cover the planets and our Moon, since they appear to lie within the ecliptic (which encompasses the zodiacal band). The band is not really a "plane" but if you bisected it with a plane you'd have the average orbital plane of the planets in the Solar System.

But as the Solar System orbits the center of the Milky Way, it does not remain in the plane of the Milky Way, but "bobs up and down" above and below that plane, like a cork in a pond riding on ripples of water.

If you're seeking to understand the orbital relationships that appear in the night sky, a text on celestial navigation or coordinate systems will help. Check your local library. In particular, James B. Kaler's aptly titled The Ever-Changing Sky has excellent diagrams and descriptions I think you'd find very informative.

Let me cast about for some diagrams online ...

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

www.3rf.org

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Posted by chipdatajeffB on Saturday, July 17, 2010 1:08 PM

From Wikipedia, here's a good illustration of the celestial coordinate system showing the plane of the Milky Way and the plane of our solar system given as the Ecliptic, the band in which the planets orbit the Sun.

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Posted by chipdatajeffB on Saturday, July 17, 2010 1:15 PM

Remember that the Earth's axis is tilted 23.44 degrees relative to its orbit around the Sun. That tilt causes our planet's north celestial pole to be inclined relative to our orbital plane. Furthermore, the gravitation "tugs" on Earth from other bodies in the Solar System causes the orientation of our planeet's polar axis to precess, with a period of about 26,000 years.

Here's an illustration from the Wikipedia article on precession:

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

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Posted by chipdatajeffB on Saturday, July 17, 2010 1:18 PM

There is another sort of precession, called perihelion or apsidal precession, which occurs because the orbits of the planets in the Solar System are not perfect circles, but ellipses. This causes the orbits themselves to change relative to the Sun (within the separate planets' orbital planes).

Here's an animation from the Wikipedia article:

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

www.3rf.org

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Posted by chipdatajeffB on Saturday, July 17, 2010 1:29 PM

The combined mass of all Solar System bodies also tugs at the Sun, causing its polar axis to precess, as well. In addition, Since Jupiter represents more of this mass that all other such bodies combined, we use Jupiter's orbit as the 'average', or what we call the invariable plane.

The Solar System's "bobbing" motion relative to the plane of the galaxy has a period of between 20 and 25 million years.

In addition, the trip around the galaxy takes our Solar System about 220-250 million years.

So, any "static" diagram illustrating all these orbits and planes is likely to be "correct" for quite a while, but is constantly changing--even on short time scales.

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

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Posted by rlh99 on Sunday, March 06, 2011 4:15 AM

I realize this is an old thread, but it relates exactly to my questions, so I hope no one minds me resurrecting it. For the first time in my life, a couple of weeks ago I held a start chart in my hands and looked at the night sky. After sorting out what I was looking at I immediately started trying to visualize relationships, the meaning of life, and everything... so I asked Google. This thread was the first that really started to answer my question, especialy Dave Mitsky's link to http://www.telusplanet.net/public/fenertyb/solsysGC.html, and then when chipdatajeffB showed the illustration of the celestial coordinate system from Wikipedia I thought that I had it sorted. But then I continued reading other articles (always dangerous when you think that you already have the answers down pat) and I find things that seem to conflict with the Wiki drawing. I am probably misunderstanding things, so I hope that someone here can set me straight on the following points;

1. The wiki drawing shows the ecliptic plane passing through the galactic centre. I thought that it was defined simply by the plane of the sun and planets of our system, and even though Fenerty's drawing does show it approximately aligned with the GC, I would have thought it a considerable coincidence if it actually did do so.

2. Similarly, the wiki shows the celestial equator and the NCP being centred on the GC, whereas I thought they were based entirely on the earth's axis and equator.

Hoping for an answer that I can understand...

Roger.

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Posted by Centaur on Wednesday, March 09, 2011 10:56 PM
 
Welcome to the discussion group, Roger.
1)   The galactic center is actually nearly 6° south of the ecliptic.  It plays no part in defining the ecliptic. 
2)  The format of that Wikipedia diagram can lead to confusion.  The celestial equator is centered on the Earth, not the galactic center.  The north celestial pole lies about 27° away from the galactic equator.

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Posted by rlh99 on Friday, March 11, 2011 5:10 AM

Thanks Centaur,  I think I'm starting to get my head around it. I've gone on to reading up on Right Ascension calculations, which has led into Time systems etc etc. I just *know* that I'm going to have questions about that. In fact, I have several right now, but when I try to write them down I get the feeling that I don't understand enough to even ask the right question to answer my confusion. If that makes sense! I'll give it another couple of weeks and see where I'm at, then.

Regards,

Roger

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Posted by DaveMitsky on Friday, March 11, 2011 10:46 AM

See http://www.thinkastronomy.com/M13/Manual/common/galactic_coords.html for an explanation of the galactic, as opposed to celestial, coordinate system.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by TropicOfTaurus on Friday, March 11, 2011 4:45 PM

Let's say a Long Term Viewer, placed in the center of our galaxy , could watch the sun, and it's entourage of planets, making this quarter billion year trip with respect to alignment against a "deep field",.  Is it not possible that , like viewing the rings of Saturn, from Earth or the Sun... There should be two periods when the solar system (sun's 'rings") are viewed Edge on?  and 2 other times they are wide open as possible... ?

Pluto excepted...

 

Hard to contemplate we've only done this as a solar system a handful of times!   

 

 

 

X   Big Smile

 

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Posted by Centaur on Friday, March 11, 2011 4:56 PM

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Yes, very perceptive.  That would be true assuming that the invariable plane of the solar system is truly invariable.  The ecliptic plane wobbles a few degrees in inclination relative to the invariable plane over periods of tens of thousands of years.  The same is true for the other planets.

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Posted by TropicOfTaurus on Friday, March 11, 2011 7:23 PM

Thanks, Centaur, I wish to retract/ or  clarify ... 1.  The Tug on our solar system by interloping effects of other stars and clusters , and shudder to think (Dark Matter,energy)? As we go around.  And 2, As Humans, or small critters that led to our presence as we know it, WE haven't been around Once!  Maybe 1/4,  or so. ?

Finally, The planets, Venus-Neptune, fairly well describe a narrow band of orbits.  Wondering now, if the whole structure is tugged , especially while orbiting some elliptical path, dipping and bobbing against the plane.  Arcturus is famous, for one, for being kinda different.    Always wonder, In the direction of the Great

Attractor, Is the Virgo Cluster kinda Whirling , orbiting in? And WRT to Andromeda, and Any Deep Field reference, Who's moving faster.   Are we being tugged by Andromeda into kinda an orbit with it, or just minor perturbations.   PS - We're safe here in Kihei,  I can keep LOOKIN UP!    Thanks,  Terry

Help me JeanMeeus,  but you're not my only hope!

X   Big Smile

 

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Posted by rlh99 on Sunday, March 13, 2011 12:12 AM

@DaveMitsky   Thanks immensely for that link Dave. I never cease to be amazed at how I can read something simple and straightforward yet fail to assimilate the facts. I already had a picture of the galactic coord system (but not your 3-D view) and my brain had obviously decided something like "... yes, yes, ok, GCS, polar axis down through the centre of the galaxy, equator  in the galactic plane, 0-deg longitude towards the sun, simple ...". So simple, in fact, that when Chipdatajeff's Wiki illustration link showed the GCS exactly the way my brain expected, I totally accepted it. And that, of course, is why I was having so much trouble in understanding how 'our' NEP and NCP could be described in the GCS. You have dropped a great shroud from my eyes...Smile

Thanks, mate,

Roger 

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