What is our Solar System's orbital plane around the Milky Way?

woolf

The topic of crossing the "galactic plane", coinciding with the Mayan calendar, and the catastrophe of "world's end in 2012" are a mixed muddling of mythology.

The Mayan calendar comes to an end (in linear counting mode) in 2012. However, the calendar itself is a circle and the Mayans thought in this circular pattern, much the same way astrology and the Chinese calendar are cyclic patterns.

Crossing the galactic plane is speculation, but also a cyclic event. Much is still unknown about the electrical nature of the cosmos as far as "action at a distance". The concern from some theorists is that the "plane" transit is related to our magnetic field shift, which is also a cyclic pattern. Since we've only inhabited this rock as semi-sentient beings for a short time, we have yet to experience that effect first-hand.

Hard data is difficult to find and there is a lack of consensus among those who are "supposed" to know these things...

I'm just a knucklehead...

woolf

mgb_phys

It doesn't end it just clocks around a new leading digit (from 12 to 13), it last did this in the 17th century and nothing happened.

Not speculation, our orbit around the galaxy is inclined - we must cross the plane twice in each rotation.

Apart from the complete lack of any mechanism to link these, the galactic orbit period is 220Myr and very regular.
Magnetic field reversals are not at all regular (and are probably chaotic) but occur at an interval of < 1Myr.

But lots of other species have and don't seem to have been over worried.

payne74

Have you ever looked out into the night sky and seen the Milky Way Galaxy? Did you notice the obvious tilt? It is at a steep angle to the straight line of the horizon. Why? It turns out that our solar system appears to belong to another galaxy that is colliding with the Milky Way. This was recently discovered when scientists were trying to figure out sources for "Dark Matter" that would account for forces we can measure but not see visibly. Using near-infrared a huge sister galaxy circling the Milky Way was discovered. It's called the Sagittarius Dwarf Galaxy,(SGR for short). For those keen on the 2012 data, this is the reason our entry point to the rift, center, heart of the Milky Way is thru Sagittarius. The two collide at this point. This explains why our solar systems is at a angle to the plane of the galaxy and why we dip above and below that center line every 12,000 years or so. After slow, continuous gnawing by the Milky Way, Sagittarius will be whittled down to the point that it cannot hold itself together much longer!

Janus

There is no evidence for, and quite a bit against the idea that our Solar system was ever a part of the SGR. Any articles that say the contrary are a result of sloppy journalism and misrepresentation.

LURCH

I don't think they are confusing to separate phenomena, but rather stating the same thing in two different ways. As an example, some might say this…... And conclude that the earth "is passing through" galactic plane. However, anyone who's taken their first year of geometry will tell you that a plane is 0° in width. Now, the exact location of the galactic plane may not be well known, but it most certainly does exist. The galaxy is rotating, and for all rotating objects there is both axes of rotation and a plane of rotation. Astronomers can have some hazy ideas as to the amount and distribution of mass in the galaxy, and those ideas might even be completely wrong. This could render our calculations as the galaxy's center of mass (as an example) to be completely inaccurate. Nevertheless, the galaxy most certainly has a center of mass. It also has an axis of rotation and a plane rotation.

For those who talk about the "plane of the galaxy" as an actual plane, we can be fairly certain that the earth has passed through it. For those who use that term to refer to the general area of increased star density of the galaxy, we are passing through it. Just a difference in semantics, I think.

Chronos

Amusing. The 26,000 year cycle relative to what? Earth completes a 26,000 year wobble cycle every second, minute, hour, day, month ... etc. It would be an eerie coincidence if earth's precessional cycle coincides exactly with the frequency the sun crosses the 'galactic plane' Just how often does this happen? I believe an 'alignment' event also occured in 1998 - so it appears an earth-sun alignment with the plane of the galactic center can occur in as few as 14 years apart. Read between the hoof prints.

CosmologyHobbyist

I recall reading that periodic mass extinctions of life may be caused by the sun's orbit of the galaxy, when the orbit crosses through the galactic plane. This crossing of the galactic plane happens every 120 million years, twice during each 240 million year orbit. The greater density of objects in the galactic plane causes gravitationally-induced perturbation of the Oort cloud, which then rains down a comet bombardment on the earth. Since the dinosaurs vanished 65 million years ago, I dont think we will get back to the galactic plane by 2012! Also, I would expect the duration of the crossing to last on the order of a million years, because the galactic plane is 1000 light years thick (galactic diameter is 100,000 light years).

mgb_phys

Except none of them actually match the period /phase of the crossing.
The sun doesn't move in a perfect plane relative to the galaxy, it wobbles above and below it's incline - these wobbles may be linked to extinction events. But if you are free to choose which wobbles you want to include then you can get them to match any sequence of events you like.

The Sun's inclination to the plane isn't that high - we don't go all the way out of the disk. We are almost in the middle of the 1000 lyr thickness, it's just that we go from a few 10s lyr above a nominal plane to a few 10s lyr below it

Redbelly98

Not sure if we are thinking along the same lines, but, it seems to me there is a sensible definition for "the galactic plane", even if if it's location cannot be measured accurately.

Our galaxy has angular momentum, which determines a rotation axis; the galactic plane would be perpendicular to that axis. Our galaxy also has a center-of-mass, which would lie within the galactic plane.

Since we can in principle specify the plane's orientation as well as a point that it contains, the plane is defined. However, actually measuring the necessary quantities (angular momentum and center-of-mass location) are another matter.

mgb_phys

We do define 'a' galactic plane, it's the basis of the galactic coordinates
It's not quite accurate, for instance the black hole at the centre of the galaxy isn't quite at 0,0

Defining the exact plane is tricky because it becomes a question of which objects you count as being in the galaxy (eg the LMC/SMC) and how far out you include the halo.

Redbelly98

Of course, we need to define a plane for the purposes of defining coordinates of celestial objects. Is it accepted practice to refer to it as the galactic plane? Sorry about my ignorance.
I concur, one would need to be clear about what objects are included. I myself am unfamiliar with the mass distribution and properties of the halo. And there is the issue of dark matter; do you (or anyone else) happen to know how well it's distribution within the galaxy is known?

mgb_phys

We pick the sun and the centre of the galaxy as two points to give a coord system
http://en.wikipedia.org/wiki/Galactic_coordinate_system

The mass distribution of the galaxy is pretty well known from rotation curves, at least as far out as we can see stars.
The centre of the galaxy is pretty well defined, it helps that there is a couple of million solar mass black hole there! The extent of the galaxy is like defining the edge of the atmosphere - it's pretty wooly.

LURCH

yeah, that's pretty much what I was thinking.

CosmologyHobbyist

Dear MGB,

Thanks for the info on sun's journey within galactic disk - you are better than Google! You surprised me when you said we are near the midway point within the disk. A look at the Milky Way or photo of same shows a very obvious half-dome marking the half of the spherical galactic center that shows above the dust lanes; the other half of of the galactic center shows as mostly obscured by dust lanes. Are the dust lanes themselves are below (or above?) the mid-point of the galactic disk?

On the sun passing through the galactic disk, when I Googled that one, the real story is that mass extinctions line up with the one end of the "bar" of our barred spiral galaxy, passing by our sun. Another view is that a spiral arm passes through the area of our sun. The time periods match within 50% margin of error, so its not definitive, but still a possibility. In my original post I didnt want to get mired in all that detail, thanks for calling me on that - I hate laziness!

payne74

The evidence is there for the ideal that our Solar system was a part of SGR. It's sloppy to say that it's misrepresentation! There's still no explanation of why the Milky Way is viewed at a angle in the night sky.

Chronos

Quote your source and then we will talk.

GESolar

This article is about the Sun and its planetary system. For other systems, see planetary system and star system.