Uncle John here: Last time I posted I asked whether we were crossing the plane of the ecliptic of the galaxy and was informed that we were not. Thanks for that.

Now I run into another story that our solar system is not even a member of the Milky Way. This seems extreme. Any thoughts would be appreciated. Internet article follow:

An incredible story, if valid. We actually belong to an overarching Sagittarius Dwarf Elliptical Galaxy and not really the Milky Way, which we are in the process of "joining," or "marrying", depending on your point of view.

http://viewzone.com/milkyway.html

There goes the neighborhood!

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

I just came to hear your band.

Seriously, I thought that the Solar System was on an inner "knob" of one arm.

The OP theory is that the Sag and Orion "arms" are actually wisps of a small galaxy sucked into the central MW and stretched into arms. I think.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

I could believe that.

So, that means we're all extragalactic aliens! Cool!

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

The Sagittarius Dwarf and its interaction with our own galaxy is real. But notice that none of the scientists quoted makes any statement to the effect that the Sun is part of the Sagittarius Dwarf; they say exactly the opposite: "For only a few percent of its 240 million-year orbit around the Milky Way galaxy does our Solar System pass through the path of Sagittarius debris. ... Remarkably, stars from Sagittarius are now raining down onto our present position in the Milky Way. Stars from an alien galaxy are relatively near us." (My bold.)

The claim that we're part of the Sagittarius Dwarf seems to originate with "Matthew Perkins Erwin ... researcher, technogeek, inventor, and recording artist", who evidently can't read his own references, and who stirs in an amazing quantity of technobabble on global warming, the galactic plane and the Mayan calendar. The signal-to-noise ratio on his blog (linked from the referenced site) is catastrophically low.

Grant Hutchison

So; Orion Arm = native, Sagittarius arm = captured galaxy.

Hmm.

Orion Arm RULES! Saggie arm drools! Whoo! Whoo! Whoo! Milky Way all the way!

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Sorry, it's a pleasing idea, but no.
The Sagittarius Dwarf has nothing to do with the Sagittarius arm: its central portion just happens to lie in the same direction as the Sag arm, but it's on the far side of the galaxy from us. It's trailing a big sparse spiral of stars as it is tidally disrupted by the Milky Way, but that spiral doesn't follow the spiral structure of our galaxy, as the diagram on the linked page shows: instead, it arches out of the galactic plane and then drops back in again at around our location.

Grant Hutchison

Then why confuse things by naming them both Sagittarius? It's like Peachtree in Atlanta.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

It seems to be customary to name galaxies orbiting our own after the constellation they lie in: so we already had a bunch of local dwarfs with names like Leo I, Leo II, Fornax and Ursa Minor when the Sagittarius dwarf was discovered.

Grant Hutchison

I have looked briefly at that scenario before and realized that Sag/dwarf was on the opposite side of the galaxy and that if that were happening ~125,000 years from now, that it could definitely impact 'our neighborhood' in some pretty profound ways.

Are you saying that they have been able to determine where Sag/dwarf was ~125,000 years ago robustly enough to ~know where it will be ~125,000 years from now?

__________________
RussT
________________________________
Everything is, as it should be, otherwise, it wouldn't be!

I'm not saying that, though it might be true for all I know.
But what is being reported is that the tidal trail of stars pulled out of the disintegrating Sagittarius dwarf galaxy is visible in the 2MASS data, and it exists as a sparse arch from one side of the galaxy to the other, passing through our current neighbourhood.
You can look at the data yourself, in a 3D flyround, at the bottom of this page.

Grant Hutchison

Has the SagDwarf core ever passed through our part of the galaxy before? Or will the next 125,000 year visit be the first time?

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

It's said to have passed through the galactic plane many times; its exact orbital history is difficult to nail down exactly.

Grant Hutchison

Thanks Grant. That does give a very different perpective from the one I had!

Which is why I said 'Brief Look'. I either assumed or thought I had remembered from that brief look, that Sag/Dwarf was completely gravitaionally bound to the other side of our galaxy, and that IF that had happened 125,000 years later or sooner, that that would have had a profound impact on our neighborhood.

__________________
RussT
________________________________
Everything is, as it should be, otherwise, it wouldn't be!

Uh oh, there are always redundancies in mergers.

Uncle John here: Thanks Grant. You cleared that up.

Glad to be of help.
It's interesting how the mangling of science by journalists contributed to the misapprehension repeated on your linked site, which references this piece of gibberish from Australian ABC: "The researchers determined that the magnetic field in interstellar space is propelling our solar system along at a 60-90° angle to the rest of the galaxy."
For comparison, here is the George Mason University press release that sparked the story: "Up to now, scientists have believed that the magnetic field outside of our solar system was parallel to the galactic plane. But Opher, Stone and Gombosi used two data sets to conclude that the magnetic field is actually 60-90 degrees perpendicular to the plane."

Matthew Perkins Erwin (researcher, technogeek, inventor, and recording artist) also seems to have had his ideas featured in Wikipedia over the last few days: I caught a cut-and-paste job from his website last night, although it's been reverted when I looked this morning. The Bickerpedia discussion page for the Sag Dwarf gives you an idea of the level of discourse involved in this particular claim.

Grant Hutchison

This claim has been posted on Digg today as well and it's up to the front page (with 950 diggs ). Its a good thing I've been a BaBlog addict for the last 2 years or else I wouldnt have known where to turn for more accurate information.

I fell for it the first time I read the column linked from the OP, and I am embarrassed to admit it. I was just glancing at it while practicing boring muscle memory exercises on my horn before going to real music. On a second reading I could see how the author had interspersed his inferences from other sources, apparently dubious ones, with direct quotes from the Virginia and Massachusetts teams without clearly separating them. Shamefully shoddy writing if you ask me, which of course he did not.

I was wondering why the reasonably reliable ABC put out such rubbish. Turns out it came from Discovery Channel, that explains that.

Not to mention that not a single result shows up for him on the ADS abstract server. Whoever he is, he's not a professional astronomer and has never published in a professional astronomical journal.

Ok, now, see (BTW, first time poster, long time reader) this has me all confused again.

Here I am, seeing all these articles proclaiming something that makes a lot of sense and then my wife and I start wondering about things.

As I was describing the news to my wife, her eyes lit up. For her, I'm
asking a question that I cannot answer. It went something like:

Her: "Now it makes sense! The center of the galaxy can only be seen
from the Southern Hemisphere."

Me: "Right. We've been oriented parallel to our parent galaxy's
direction of motion as it passes through the plane of the Milky Way.
The Solar System is coming in at a high angle."

Her: "What about Uranus?"

Me: "Hmm..." (mental gears begin grinding)

Her: "Wouldn't that mean that Uranus is the only planet in the Solar
System that's aligned with the plane of the Milky Way?"

Me: "You know what? Let me ask around and see if I can give you an
answer that's trustworthy."


So that's where I am and that's why I'm here.

Let me know if I should be telling my kids really cool stuff like they're invaders from another galaxy.

I'm serious, guys. Get this straight for me or so help me I'll turn my kids loose in that moronic Creationist "museum" and send them to Florida to learn how to vote.

It seems there's no significance in the fact that the galactic plane is tilted relative to the plane of the solar system and relative to the plane of Earth's equator, and no reason to predict that the plane of the solar system should match the plane of the galaxy. If we look around at multiple star systems, we see the planes of their orbits are arranged at all sorts of angles to the galactic plane; it seems that what must influence the plane of rotation of a star system is the random motion within the cloud it forms from, rather than the rotation of the galaxy as a whole.
So: the tilt of the Milky Way in the sky isn't telling us anything significant about the solar system's origin.

As to the axis of Uranus, it turns out not to be aligned with the galaxy's axis: the galactic north pole points towards the constellation Coma Bernices; Uranus' north pole points between Orion and Taurus. The separation between the two axes must be around 120 degrees.

Grant Hutchison

As for galactic collisions et al, it's important to relinquish one's terracentric views and realize that space is just that. There's very little matter out there.

Kind of like driving through a hailstorm where each hailstone is about 87 miles from the next one.

__________________
A person's name, or a mark representing it, as signed personally or by deputy, as in subscribing a letter or other document.

As a sign of appreciation for your answer, I'll make sure my kids never get near that museum (unless they're toting cases of eggs and toilet paper). The Florida voting thing was an empty threat.

Meanwhile, thanks also for the ikipedia link. I wonder if watching debates regarding subjects such as this can be considered a "spectator sport"?

Thanks. I only did it to save the kids.

It's certainly a good way of adjusting how much faith you might have in a given article: if you find a couple of single-issue loons hacking lumps out of each other on the discussion page it does make you wonder rather a lot about the information being provided.

Grant Hutchsion

The webpage is undated, a truly annoying habit. However, it does refer to a 2MASS study from 2003, and Steven Majewski and a paper in The Astrophysical Journal. That is almost certainly Majewski, et al., 2003, where they say "The Sun lies within a kiloparsec of that plane and near the path of leading Sgr debris; thus, it is possible that former Sgr stars are near or in the solar neighborhood." That's a far cry from claiming that the sun came from the Sag dwarf. However, see Newburg, et al., 2007, which has been accepted for publication in The Astrophysical Journal. In this paper they say, "We show that the Sagittarius dwarf leading tidal tail does not pass through the solar neighborhood; it misses the Sun by more than 15 kpc, passing through the Galactic plane outside the Solar Circle."

So, I wouldn't get too worked up about the sun coming from some other galaxy; as far as I can tell, nobody said that except maybe the webpage author. Furthermore, there is clearly some debate about where the Sag dwarf tidal tail really goes.

__________________
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell